- "You might both be killers Oliver, but he's a psychopath."
- —John Diggle to Oliver Queen on Adrian[src]
Simon Morrison (April 21, 1986–May 17, 2017), known under the alias Adrian Chase, was the former district attorney of Star City and a former close collaborator/friend of Oliver Queen as mayor, helping him in cleaning up the streets through the legal system. He was the serial killer who was calling himself Prometheus, and not only knew that Oliver is Green Arrow, but had a personal vendetta against him as well. Having lost his father four years ago at the hands of the Hood, Adrian desired retribution, and spent his time afterwards studying The Hood's skills and history, while also uncovering Oliver's true identity as Green Arrow. In his alter-ego, Prometheus crusaded against Green Arrow in order to destroy the vigilante's life and legacy. He had also been labeled by the media as the "Throwing Star Killer" for murdering people whose names formed anagrams of individuals on the List using shurikens made from Oliver's discarded arrows as a form of sending a twisted message to him.
Eventually, Chase was defeated by Oliver where he was temporarily taken into custody by A.R.G.U.S.. After a short time spent in a glass walled prison, he managed to escape to Lian Yu. After facing off with Oliver in battle once again, he was defeated and then proceeded to die by suicide. His death triggered the detonator which in turn set off all of the hidden bombs situated throughout the island.
Simon was born on April 21 1986 to Justin Claybourne and an unnamed woman with the surname Morrison who would later change her name to Amanda Westfield. Little else is known of his earlier life but he apparently grew up to be a psychopath according to his father's lawyer.
Preparing for his crusade against Oliver Queen
In late 2012, Simon's father was murdered by the Hood, and so he sought vengeance upon the elusive vigilante. Dropping off the grid completely and erasing all traces of his existence from the internet, and changing his name to "Adrian Chase", Adrian researched his target and learned everything he could about him. In his research, Adrian discovered the identity of his target as Oliver Queen and obsessively studied him, learning everything he could about him and his allies. In his research he became aware of the existence of The List, a book of Starling City individuals with ties to Malcolm Merlyn, which included Adrian's father who Oliver had targeted. This led to Adrian believing that Oliver was really a serial killer and his righteous crusade was a lie to justify a killing spree, and therefore poisons the lives of those he cares for, and swore to make him suffer. At some point he met and fell in love with a woman named Doris, who later became his wife.
In early 2015, after learning much about Oliver's life, Adrian sought out Oliver's former mentor Talia al Ghul to learn the ways of the League of Assassins. Impressed that Adrian deduced Oliver's identity on his own, Talia accepted his request, as she was now equally vengeful towards Oliver as he had killed her own father Ra's al Ghul. Through Talia, Adrian also learned more about Oliver's past including his activities on Lian Yu, in Hong Kong and in Russia. He also became aware of Oliver's son William Clayton. Presumably through his affiliation with Talia and her own resources Adrian also became aware of the existence of time travel and the multiverse. He also became aware of Team Flash's pipeline prison and the Waverider indicating that he is aware the identities of Barry Allen/The Flash and the Legends led by Sara Lance/White Canary.
After acquiring the skills needed from Talia, Adrian armed himself with an array of weapons forged from The Hood's discarded arrows kept in the Star City Police Department evidence lockup. Adrian also began using a suit strikingly similar to Oliver's suit from his days as the Hood, but with darker colors and with a full face mask, adopting the name "Prometheus". Adrian chose that name because of Prometheus' role in Greek mythology in taking away power from the judge, jury and executioner gods. After Oliver became mayor Adrian became a lawyer and eventually succeeded Susanna as district attorney of Star City to get become personally acquainted with Oliver and keep closer tabs on him. Adrian was building a case against Derek Sampson with the intent of flipping the drug dealer so he'd give up the names of his suppliers.
Beginning his crusade
Five months following Damien Darhk's death, Adrian began his crusade by targeting individuals in Star City whose names formed anagrams to other names on The List. His first target was Lieutenant Conahan. When Conahan was leaving the SCPD precinct, he noticed Prometheus on the rooftop. Mistaking him for Green Arrow, Conahan asked if he could help him, but was shot by an arrow. Conahan painfully tried to shoot back, but Prometheus dodged his shots, leaped to the ground and threw a shuriken to disarm him. As Conahan tried to flee, Prometheus threw a knife into his leg, knocking the cop down. As Conahan desperately tried to crawl away, Prometheus slowly walked up to him, sword in hand, and, when asked if he was Green Arrow, coldly replied that he wasn't and killed him.
Conflict with Tobias Church and meeting Oliver Queen
A few nights later, Adrian learned of Green Arrow's encounter with crime lord Tobias Church amidst his illegal deal with AmerTek Industries, where he almost killed Green Arrow. In response, Prometheus stalked Church and as he left Club XLR8, and killed his two bodyguards. While Church mistook him for the Green Arrow and laughed in amusement, Prometheus threw an axe into Church's shoulder, leaped to the ground and slammed Church into the pavement. Prometheus angrily told Church he was aware of his attempt to kill the Green Arrow, and warned Church that the former was his to kill and if he ever tried to do it again, then he'd die as well. 
After learning that Oliver's ally Rene Ramirez supposedly killed Derek Sampson, Adrian went to confront Oliver about it (officially becoming acquainted with him) and told him about what happened to Sampson. After Sampson turned out to be alive, Adrian asked for Oliver to get Judge Pittson to allow Adrian to obtain a warrant to search his known hideouts. After he agreed, Adrian told Oliver about the first time they met, when Oliver picked up his girlfriend, but he ironically reassured Oliver that he doesn't hold grudges. Later, Green Arrow and his new team apprehended Sampson which pleased Adrian as he informed Oliver and Thea of this.
A few days later, during a meeting at the mayor's office, Adrian met the new deputy mayor Quentin Lance and said that working for him would be a pleasure. While Quentin was surprised Adrian told him that he doesn't blame Quentin for working with Darhk, as he had threatened his daughter Laurel. He explained public service wasn't easy and that, sometimes, getting a little dirty was inevitable in order to clean it up. When Team Arrow apprehended Sergio Espinoza, an associate of Tobias Church, and stole a package from Palmer Technologies, Adrian and Quentin personally delivered it to the SCPD evidence locker. The evidence instead turned out to be a disguised bomb, causing an explosion that allowed Church and his men to infiltrate and steal weapons from the evidence locker. 
Later that night, Adrian interrogated Espinoza at the Anti-Crime Unit headquarters, threatening to beat the information out of him due to Espinoza's refusal to talk. Initially, Espinoza didn't take Adrian's threat seriously due to his position as a district attorney, but Adrian reminded him that justice in Star City is dealt by vigilantes. Before the interrogation could go further, Church and his men attacked the ACU and killed several of the guards all while trapping Adrian and Espinoza inside the building. Suddenly, Ragman appeared and planted a bomb on the wall, and as he absorbed the ensuing explosion, Mr. Terrific, Wild Dog and Artemis emerged from the hole that was created. The team escorted Adrian and the other ACU members out of the building to safety. Later, Adrian informed Quentin and Thea of the incident but hadn't been able to find Wild Dog, who had been kidnapped during the attack. Adrian then told them that he'd re-evaluated his view on vigilantes and started to trust Team Arrow more.
Angry that Church had ignored his warnings and kidnapped Wild Dog, Prometheus confronted Church, and while attempting to kill him with an arrow, Church's bodyguard protected him from the attack. Prometheus reminded Church he had his second warning and wouldn't be given a third and left. After Church was arrested following his defeat by Green Arrow and being transferred to Iron Heights, Prometheus attacked the convoy of police cars escorting him. After slaughtering the escorting officers, he confronted Church in the police van. Church futilely tried to plead for his life by telling him Green Arrow's identity: Oliver Queen, unaware Prometheus already knew. When Church asked if they were cool, Prometheus threw a shuriken into his neck and killed him, and replied that they were, then left the scene of his slaughter.
War with Team Arrow
With Green Arrow now aware of his existence after being informed by Church prior to his death, Prometheus lured him and Spartan to a construction site, using Church's cell phone to lure them out. After they tracked the phone, Prometheus called it, heavily breathing into the phone, as Green Arrow answered. He then ignited a message on the ground, "SO IT BEGINS". From there, Prometheus continued killing civilians to form more anagrams of individuals on the List including Peter Meld and Gay Eked. Their names, along with Conahan and Church's, all spelled out anagrams of Green Arrow's previous victims: Adam Hunt, Ted Gaynor, Palmer Cokes and Sachi Beech. Adrian later went to the scene of Gay's murder where he "met" Green Arrow and told him everything he knew about the victims, Green Arrow oblivious that his target was speaking to him.
Later Susan Williams reported on Prometheus' killings on the news which Adrian told Oliver was a disaster. After Susan dubbed him the "Throwing Star Killer", Adrian admitted to a annoyed Oliver that it had a "certain flare" to it. Finding more six more potential victims after discovering Prometheus' pattern, Team Arrow sent a member to each one. Prometheus went after a train driver but was confronted by Artemis. They entered into a duel where Artemis managed to cut Prometheus' right arm, before Green Arrow came to Artemis' rescue, shooting an arrow into his back. Instantly recognizing it as an explosive arrow, Prometheus threw it onto the roof where it exploded and Prometheus escaped through the hole made, but left a bomb which blew up the train, though Green Arrow and Artemis ultimately escaped with the train driver. Later, Prometheus sneaked into Quentin Lance's apartment and left a cut on his right arm, while he was passed out from alcoholism, just like the cut Artemis gave Prometheus, and left a shuriken to implicate him.
Sometime after Prometheus' encounter with Artemis he sought her out, after deducing her identity as Evelyn Sharp. Prometheus manipulated her into betraying Oliver, as Evelyn had become resentful of him after learning he was the Hood, who'd murdered several people she knew, promising to let her watch when he finally killed Green Arrow. Recruiting Evelyn to his cause allowed Prometheus to learn the identities of every Team Arrow member, as well as information on their personal lives including loved ones. While trying to find bank robber Eric Dunn before the elusive Vigilante did, Adrian interrogated his arrested associate Laura Buser. However, she simply told him to go to hell to which he gave a cold stare and replied that he'd been to hell, and slammed his hand into her mask to intimidate her, and so she gave up Eric's location. As Adrian told Oliver that Eric was hiding out at Papp Motel and Oliver went to inform the ACU while Adrian secured a warrant to search the area. Later after Team Arrow defeated Vigilante, Prometheus met Artemis alone on a rooftop, where she assured him she wasn't followed and told him that Team Arrow didn't suspect her true allegiance.
In December 2016, Prometheus went to Central City, where he broke into S.T.A.R. Labs without setting off any alarms and freed Laurel Lance/Black Siren, the Earth Two doppelgänger of the late Laurel Lance/Black Canary, to impersonate her Earth One counterpart to taunt Oliver. Grateful for freeing her Laurel agreed to serve him and to maintain her cover, Prometheus told her vital information on Earth One Laurel's life. He also informed her of the Waverider and the Legends, so Laurel could use the cover story that Sara brought her back and transported her to the present. While Laurel was reluctant to aid him after learning that one of Adrian's targets was Quentin, the Earth One counterpart of her father, he promised to spare him in exchange for her obedience and she complied. Team Flash would be unaware of the breakout for almost 3 days.
First encounter with Green Arrow
During Christmas, Prometheus, while sharpening his weapons in his hideout, was approached by Evelyn with photographs and addresses of Felicity Smoak and Rory Regan. Evelyn then asked Prometheus to be there when he killed Oliver, but Prometheus stated that he didn't intend to kill Oliver, only to make him wish he was dead. Prometheus later attacked Curtis Holt at the mayor's Christmas party and his husband, Paul, effortlessly defeating him and injecting him with the drug, Dycloseral, making Oliver and Team Arrow aware that he knew their secret identities.
At Claybourne Pharmaceuticals, Prometheus confronted Green Arrow and engaged him in a battle, managing to hold his own for a bit and showing off a technique Talia had taught them both. Suddenly, Wild Dog shot his katana out of his hand, causing Artemis to intervene and reveal her true allegiance. As Green Arrow and Wild Dog stood in shock, Artemis fired a smoke arrow to cover her and Prometheus' escape. While investigating Claybourne Pharmaceuticals, Detective Billy Malone discovered a photograph of a baby and sent it to Felicity, before Prometheus apprehended Billy. Adrian later told Oliver of Billy's abduction and insisted that the ACU have a shoot to kill order placed on Prometheus which Oliver agreed to. Tracking Prometheus to the AK Desmond Group, where Oliver killed Claybourne, Green Arrow discovered that Prometheus had staged the hallways with bodies to recreate the scene of Oliver's victims he'd killed when pursuing Claybourne before confronting Prometheus in the exact spot in which he killed Claybourne. Prometheus asked if the Green Arrow had even hesitated when he killed him, or he was merely another name on the List, but as Green Arrow told him he was there if he wanted revenge, Prometheus replied that his crusade was about so much more than simple revenge.
They engaged in a fight before landing crashing into one of the building's floors. Secretly over a wireless speaker, Prometheus told Green Arrow that he knows everything about him and is going to show him and everyone else that everything he touches dies. Having dressed Billy Malone in his suit beforehand, Prometheus managed to trick Green Arrow into killing him in order to prove his point, telling him over the wireless speaker, attached to Billy, that everyone he loved would die. Imitating Lyla Michael's voice Adrian called Diggle and tricked him into returning to the safe-house his family were staying in, and tipped off the F.B.I. which allowed them to recapture him. After this, Prometheus sent Laurel to impersonate her Earth One counterpart, roughly 3 days after breaking her out of S.T.A.R. Labs.
Exonerating John Diggle and working with Black Siren
Eventually Laurel's cover was blown but as she asked why she couldn't have just killed them, Prometheus furiously tackled her. Choking her throat tight enough to prevent her using her scream power against him, Prometheus reminded her that her freedom and life were contingent on her following his orders. Terrified, Black Siren agreed and fell in line. Adrian was later called to Oliver's office where he informed him of John's arrest, as he'd been wrongfully imprisoned for illegal arms dealing of a nuclear trigger, set up his superior General J.G. Walker, and wanted Adrian to represent him. Adrian was initially skeptical but agreed. Adrian visited John and told him he was representing him but as Walker appeared to transport John into custody, he insisted to Adrian that Walker would simply falsify an excuse to kill him to cover his tracks. Adrian then tried to delay Walker with various regulations but Walker told Adrian he had the attorney general on speed dial, and threatened to have him disbarred unless John was placed in his custody within 24 hours.
Later Black Siren escaped Team Arrow's custody and Prometheus went to meet up with her. Encountering Ragman, he quickly knocked him out before confronting Green Arrow, which lead to another fight between the two. Green Arrow threw a drugged-dart at Prometheus before firing a cable-arrow at him, hoping to restrain and finally capture him. Instead Prometheus shrugged off the drug and reacted quick enough for the cable to wrap around his arm rather than his whole body as intended. Breaking the cables with his sword, Prometheus told the archer he had a tolerance to the drug and they continued their fight. After seeing Felicity being confronted by Black Siren, Prometheus tauntingly told him to choose between him or Felicity, concluding the ordeal by kicking Green Arrow through a wooden wall, to where Black Siren and Felicity were, before escaping as Black Siren was captured again.
To ensure John wasn't placed in prison, Adrian told John to punch him and pretended to try and fight back as his guards restrained him, having instructed them to, as Walker saw this happen. Adrian then reminded him that if a prisoner committed an offence against the district attorney within his jurisdiction, he could personally oversee the matter and reminded Walker it "could take a while". This allowed Adrian to delay John's transportation into Walker's custody by one week. Adrian discovered from a friend at the National Security Agency they were investigating Walker including his involvement with the nuke, but Walker's associates made sure the information remained classified and beyond Adrian's reach. Later, Adrian received the NSA's case against Walker from an anonymous source, and after sending it to a judge pleaded for a motion to dismiss, and was able to get John released on bail.
Oliver later held a conference to make John's exoneration public and to commend Adrian's actions. Susan Williams hoped to get an exclusive on Billy Malone's death, though Adrian told her he had no comment as he'd told the other reporters. After a gunman attacked City Hall and shot Adrian, he was taken to hospital but recovered quickly, though Doris was concerned about his well-being and tried unsuccessfully to convince him to take some more rest instead of come immediately back to work. After discovering the shooter as James Edlund, a man who had lost his family to a mall shooting years before, Adrian discussed people's rights to wield firearms with Oliver. Though skeptical to allow civilians to have easier access to firearms, Oliver eventually agreed with Adrian and after much discussion with councilwoman Emily Pollard adjusted the firearms law, allowing people better protection.
Attacking the Queen administration
After Oliver visited Adrian's mother Amanda, asking her for the name of her son, Adrian sent a letter to SCPD Captain Frank Pike containing the autopsy report for Detective Malone's true cause of death. As a result, Pike ordered the Anti-Crime Unit to arrest Green Arrow for Billy's death. Adrian was later present when Oliver and Quentin tried to convince Pike that the Green Arrow was innocent, though he initially refused to listen as he'd still killed a member of ACU. Despite this, Oliver was successful in getting Pike to stop his pursuit after talking sense into him. After this, Adrian leaked the mayor's office's role in covering up Billy's death to the media which was then broadcasted by Channel 52 News, in order to end Oliver's administration as mayor.
Discrediting the Green Arrow and discovered by Team Arrow
Adrian offered his letter of resignation in order to take full responsibility for the cover up, but Oliver denied his request and instead insisted that Adrian represent him as his lawyer at the hearing. While Adrian agreed, he reminded Oliver that the circumstances would call for someone to take the fall. At the hearing, Adrian and Oliver watched as the coroner confessed to filing a false report on Billy's death to Councilman Collins, and as Captain Pike told them of Oliver's vouching for the Green Arrow. After the first stage of the hearing, Oliver, Thea, Quentin and Detective Dinah Drake left for the office, though their limo was attacked by Vigilante which left them all injured. Adrian gave his reassurances to delay the hearing in light of the attack, while making Oliver accept medical treatment as he'd declined. Adrian confronted Dinah as she'd found a broken piece of Vigilante's visor and offered to take it back to the precinct for her.
Later, Prometheus encountered Vigilante on a rooftop, presumably using the tech from the visor to find him, and warned him that Oliver was his to kill, though Vigilante simply swore to kill him first and they came to conflict. Prometheus, clearly being the superior combatant, overpowered Vigilante and forced him off the rooftop, though somehow Vigilante survived and fled. Unmasking, Adrian then called 911 and informed them of a Vigilante sighting. Later Adrian talked to Pike over the various vigilante sightings and if they were simply delaying Star City's inevitable fate, though Adrian reminded him that delaying the inevitable was part of their job. As he kept Pike busy with small talk, he slipped the piece of Vigilante's visor back to Dinah.
At Oliver's office, Adrian offered to take the fall for everything, but Oliver refused to accept this, though Adrian reminded him that someone needed to be discredited or Oliver would lose his job. Instead, Oliver decided to offer up the Green Arrow. Adrian stood by Oliver, Thea, Quentin and Dinah as he gave a speech to the public discrediting Green Arrow with the murder of Billy Malone. Afterwards, Adrian informed Oliver that after his speech Collins has ruled against ending Oliver's administration. Oliver immensely thanked Adrian for this and Adrian reassured Oliver that he didn't do it just because he was his boss, but because he was a friend. Later, Adrian confronted Susan and told her he supposedly had an exclusive for her, sickly joking that it was a "matter of life and death".
After confronting Susan he kidnapped her and held her in an abandoned hotel rigged with explosives. Prometheus then filmed her tied to a chair and tearfully screaming in fear, as he held a knife to her throat, tauntingly telling her to scream for him again. Anticipating that Team Arrow would use his mother against him as leverage, Adrian had Amanda relocated and left the film of him and Susan playing on a continuous loop for Team Arrow to find. Adrian was later informed by Talia that Oliver was aware of his true identity as she had told him to make him suffer, though Adrian was glad Oliver now finally knew. As Adrian was in a board meeting discussing the drug trade Oliver returned though Adrian discreetly taunted him about his inability to confront him, asking if he's "been asleep this whole time".
Later Green Arrow confronted Adrian in a parking garage, firing several arrows at his car in a failed attempt to intimidate him, but Adrian was disappointed that Green Arrow wanted to arrest him instead of kill him. However, Green Arrow firmly told him he wasn't going to kill him if only that's what he wanted him to do. Adrian then told Oliver her had Susan hostage but warned him that if he dies or doesn't get back in time, Susan will die of starvation and dehydration, nor was he concerned with the idea of torture as it would have the same results. Powerless Green Arrow let Adrian go as he pridefully taunted him that he was 10 steps a head of a game Green Arrow still didn't understand and laughed as he left the scene.
Later Adrian ran into Quentin and Rene, also now aware, and told them he liked it better with them knowing who he is now. While they promised to kill him Adrian taunted them by reminding that threatening a city official was a felony and that he was only getting started with his plans, and reminded them to get back to work leaving them powerless to do anything. Anticipating that Oliver would try to use Doris as leverage Adrian tipped the ESU and they arrived in time to confront Green Arrow, and stopped him from getting near Doris. Adrian later attended a press conference to inform the public of Green Arrow's "attempted kidnapping" of Doris as retaliation for his recent "crimes". Because of this Oliver was forced to publicly order Green Arrow to be brought in within 24 hours, or the S.C.P.D. would hunt him down. However this was also a discreet threat to Adrian himself.
After somehow learning that Oliver gave information on his original identity to Captain Pike, Adrian approached him disguised as a homeless man and stabbed him putting him in a coma. Adrian visited Pike in hospital as Oliver arrived who promised that he would kill Adrian as soon as Susan was found. Adrian wasn't threatened by his words and reminded Oliver that if he died Susan would be dead too, as much as Moira, Tommy, Shado and Laurel are, and taunted him that one more loss may just destroy him but taunted Oliver that if he killed him, then he'd only really be killing himself and losing any sanity he has left.
After Team Arrow finally located Susan's location Prometheus was waiting for Green Arrow and he unmasked and noted that he was glad that knew as he preferred it face to face. While Green Arrow threatened to keep them inside until the entire building exploded Adrian deactivated the bombs. However Adrian was caught off guard when Spartan arrived with Doris and exposed his identity to her, proving Adrian really is not ten steps ahead. Despite her attempts to reason with him Adrian told her he will stop but stabs her to protect his secret and continue his vendetta. Green Arrow attacks him in anger and the two proceed to fight. After a heated battle that ended in a draw Adrian told Green Arrow neither would kill the other. Oliver said he could kill Chase but before he could even try, Talia injected him with a tranquilizer arrow and the two kidnapped Green Arrow, taking him to an unknown location.
Adrian later returned to the precinct as Quentin was escorting Susan in for a statement, giving his "sympathies" for her as Quentin threatened him again. However Adrian asked him not to threaten him as he was in mourning, as Green Arrow "killed" Doris, though Quentin and Susan swiftly saw through his lies. However Adrian also reminded them he had Oliver and threatened Quentin and Susan that if they tried anything, he'd send Oliver back to them in pieces. While Susan did still give a statement to the police Adrian had an airtight alibi so they didn't believe her and Adrian's cover remained intact.
In Oliver's holding cell Adrian watched Oliver futility trying to reason with Talia who then told Adrian to make him suffer, which he happily agreed to. As Oliver promised Adrian his friends would find him but Adrian simply reminded Oliver yet again that he wasn't going to kill him. He then told Oliver that he'd confessed to Susan while in captivity that Oliver had helped him discover who he truly was, and promised to help do the same for him before subjecting him to torture.
Torturing Oliver and exposure to the public
Adrian held Oliver captive and tortured him, trying to make him confess what Adrian believed to be the real reason for his killings: that he did it simply because he wanted to, using his father's wishes as justification. However Oliver didn't know what Adrian wanted and Adrian tortured him for 6 days trying to get the answer. On the 6th day Adrian held him underwater for 140 seconds, the same amount of time it took for Adrian's father to drown. When Oliver didn't "confess", Adrian resumed the torture. When Oliver regained consciousness Adrian planted photos of Oliver's victims, but as Oliver reminded Adrian they all had victims themselves, Adrian further pointed out they also had families and they all suffered because of him. He also reminded him of a memorable victim, Cecil Adams, who Oliver had killed to save Felicity 3 years ago, and he let Oliver know the Count's true name Cecil Adams.
When Oliver still didn't know what to "confess", Adrian fired three arrows into him, just like he had done to Cecil Adams 3 years prior. After pulling out the arrows, Adrian showed Oliver a pair of Felicity's glasses, having sneaked into her apartment without her knowing, to taunt him. He then showed him a picture of his son, William Clayton, and while Adrian admitted that he didn't know where William was, he promised Oliver that he would find him eventually, unless he "confessed". Afterwards, Adrian returned with Evelyn to deceive Oliver by pitting them against each other, promising to let the survivor go or he'd break Evelyn's neck, before leaving to tend to other business. When he returned he was disappointed to see that Oliver hadn't even tried, and Adrian pretended to break Evelyn's neck as she acted dead to horrify Oliver.
Returning, Adrian intensely taunted Oliver, telling him of his belief that everything: the List, the Hood and his heroic crusade; were all just an excuse for why he truly killed. Finally, Oliver cracked, angrily admitting that he had in fact killed because he liked it. Pleased, Adrian mused that he'd made him confess the one secret he wouldn't even admit to himself, as Evelyn dropped her facade and agreed with him. Adrian told Oliver that he was right, that he infected every life he touched as his crusade was based on a lie, resulting in a price, namely the death of his loved ones, and that the still-living John and Felicity would eventually pay it too.
As a reminder of the six days of torture, Adrian took a blowtorch to Oliver's chest to burn away his Bratva tattoo. Before doing so Adrian reflected that Oliver must have done something extraordinary to have earned a captain rank in the Bratva, and how the burned tattoo would now serve as a reminder of his confession. As Oliver tearfully tried to apologize, Adrian accepted the apology but informed Oliver he simply didn't care and burnt away the tattoo, causing Oliver to pass out from the pain. Adrian then left while Oliver was passed out and left his uniform and equipment behind for him, leaving the door open for him as promised.
The next day Adrian visited Oliver in his office, thanking him for "granting him leave" to mourn for Doris' death while Quentin angrily threatened him. When both were alone Adrian gave Oliver a knife and presented an ultimatum; to either kill him as Oliver Queen in broad daylight, as he couldn't reach him as Green Arrow now that he was in protective custody since Green Arrow "murdered" Doris, or let him go knowing there is nothing he can do. Ultimately Oliver declined Adrian's offer, much to his disappointment, and told him to keep the knife as he left. Later Adrian's protective custody escort was attacked by Bratva agents hired by Oliver previously but Team Arrow intervened and Adrian used this chance to escape. While he was briefly confronted by Curtis he swiftly overpowered him, tauntingly asking how Paul was, before Curtis was forced to flee.
In light of the Bratva attack S.C.P.D. decided to transport Adrian into F.B.I. custody and asked Oliver for his approval. Unable to decline without arousing suspicion Oliver agreed and told Adrian, despite his insistence otherwise, that nothing was more important to him than his safety. Before Adrian was transferred he quietly expressed amusement at what Oliver did but Oliver quietly promised that they weren't done and Adrian was transported into custody of the US Marshals. Later as Adrian was writing while in protective custody, he heard his bodyguards receive a message and somehow immediately deduced he'd been exposed. He swiftly threw his pen into one guard's eye before strangling the other to death. With his secret identity exposed and his plans ruined by this setback, Adrian then repeatedly stabbed the first guard to death viciously in frustration and left the safe-house. As Adrian was driving down the street, watching the convoy of S.C.P.D. officers going to arrest him drive right past him, he whistled to the radio as he made his way back to Star City, still splattered with blood.
Tuberculosis plot and capture
After arriving back to Star City he lured Team Arrow and the S.C.P.D. to a video game arcade but rigged all the attractions with weapons and rigged one of them to display an image of Prometheus and the words "GAME OVER". Somehow Adrian caused an EMP explosion in the Arrowcave which left Oliver and Felicity trapped for sometime forcing Team Arrow to focus on getting them out. While they were distracted, Adrian tracked down Oliver's son William and told him he knew his father and presumably kidnapped him. Because of Adrian's exposure to the public as a serial killer all convicts he detained were released after retrial which including Sampson. Adrian soon enlisted Sampson's aid to seemingly recreate his father's tuberculosis outbreak by having him steal the chemicals required.
While having Sampson obtain these chemicals Adrian distracted Team Arrow while also ruining Oliver's memory of his father by sending a crate containing the encased body of Councilman Henry Goodwin which exposed Robert's role in his death to the public. Anticipating that Oliver would confirm the origin of the cement encasing Goodwin's body came from Oliver Enterprises, Adrian rigged one of the hallways as traps which Oliver and Diggle fell into. Falling into a secret room Adrian set up raw cement to flood the room and kill them in the same manner Goodwin died, though Dinah and Curtis were able to save them at the cost of Sampson obtaining more chemicals for Adrian's plan. Anticipating that Oliver would seek out Claybourne's lawyer Darren Coffman for answers Adrian gave him a USB stick containing footage of Robert killing Goodwin to tarnish their memory of their father.
After obtaining all the components Prometheus had Sampson and his thugs rig a device to disperse tuberculosis on a city-wide scale. When Team Arrow attempted to stop the plan Prometheus ambushed Green Arrow, Spartan and Mr. Terrific but Green Arrow managed to keep Prometheus distracted long enough for Spartan and Mr. Terrific to make their way to the roof and they along with Dinah and Wild Dog foiled the plan and stopped Sampson. Meanwhile Prometheus continued to fight Green Arrow as their fight carried out down two flights of stairs with both combatants being fairly evenly matched. Unmasking, Adrian taunted Green Arrow that he couldn't kill him and that their father's legacies are what led them to becoming who they are.
However Green Arrow revealed to Adrian that Claybourne, prior to his death, was going to disown him not because he was illegitimate but because he believed him to be a psychopath. Seemingly crushed to learn this Adrian collapsed to the ground in grief and offered Green Arrow his sword and begged him to kill him. However Green Arrow refused but told him he was going to face justice and knocked him out. Adrian was taken into A.R.G.U.S. custody and watched Oliver on live television with a smile on his face while Oliver confessing to the city that Robert had sacrificed himself to save Oliver's life 10 years ago, in an attempt to somewhat preserve Robert's legacy.
Meanwhile he had Evelyn break Laurel out of A.R.G.U.S. and had them co-ordinate with Talia to kidnap every Team Arrow member once he was incarcerated in preparation of his endgame.
While being incarcerated he set orders to his team to kidnap Oliver's teammates to which Oliver came to his cell and asked him about the whereabouts of his team to which he replied that if he wants his team to be safe he has to be released from custody. Adrian also told Oliver that he would be receiving a phone call, a call Oliver received moments later showing a kidnapped William. Oliver decided to comply with Adrian's demands and along with Malcolm Merlyn helped him escape as he was being escorted by A.R.G.U.S. agents to a helicopter to be transported elsewhere. Adrian then used the helicopter to escape so he could take a plane to Lian Yu along with both his team and Team Arrow. While there, Adrian taunted Team Arrow and told them that he would be waiting for Oliver to show up.
Battle on Lian Yu and death
Adrian, Black Siren and Talia's acolytes had confronted Oliver, Team Arrow, Nyssa and Deathstroke. Adrian then taunts Oliver about his son and duels with him as the rest of the team take on the acolytes and Black Siren. As they dueled, Oliver threw Adrian off the balcony and attempted to break his neck, only with Adrian goading Oliver to do so. But Oliver gives up in the end, stating that while Adrian can blame him for his father's death for the rest of his life, Oliver has already forgiven his sins. Adrian once again tries to goad Oliver into killing him by lying to him that his son was dead, but Oliver saw right through him and told him even if it were true, he would never let him get the outcome he wants. As Oliver turns to leave, Felicity alerts him that Adrian had initiated a dead man switch that would blow up hundreds of C4 bombs planted all over the island as he escapes using a smoke bomb with Oliver close in pursuit, only to find him getting away in a boat.
Oliver however is able to catch up to him and brutally beats him down. However, Adrian then drags William out which a distraught Oliver aims his bow at him, but Adrian issues an ultimatum: For Oliver to kill him so everyone on the island would die, or spare him so he would kill William. As Oliver lowered his bow, he shot Adrian's leg and he let go of William while collapsing to the ground in pain, thus saving everyone. However, as Adrian lay on the deck defeated, realizing that Oliver's decision was resolute and would never kill him, Adrian congratulated Oliver for winning and getting William back was good as it was "going to be lonely", and drew a pistol and pressed it against his head as Oliver frantically attempted to stop him from detonating the bombs. But Oliver's efforts were futile as Adrian fired the gun before he was able to reach him while grinning at Oliver, committing suicide as a last-ditch effort to break him one way or the other, triggering the dead man switch and leaving a horrified Oliver staring at him, only to turn and watch while holding William in his arms as the hundreds of C4 bombs on Lian Yu went off. Although his endgame cost Oliver the life of Samantha and landed Thea in critical condition, the rest of Team Arrow managed to survive by using his plane to shield themselves from the explosions.
Even though Adrian's endgame left deep marks within Team Arrow, Oliver and the team was able to put him and his actions aside and move on, thus his entire revenge scheme ended in failure; therefore his years of planning on getting revenge on Oliver for killing his father, Justin Claybourne, was ultimately in vain. Ironically, all of his efforts and planning on destroying Oliver only resulted in him becoming a better man than he was before.
5 months after Adrian's death/suicide, a photo of Oliver unmasked in his Green Arrow suit was sent to Channel 52, that almost successfully resulted in Oliver being outed as a vigilante, Team Arrow believes it was the final gift from Adrian.
Little was known about Adrian's personality before the death of his father, but he was believed to be a disturbed individual even before that, as his father secretly planned to disown him because of his apparent psychopathy. After his father's death, Adrian was consumed with grief and hatred for his murderer, the "Hood", and spent four years studying, training, and patiently waiting to destroy him completely. After uncovering Oliver's identity as his father's killer as well as virtually his entire history; Adrian went so far as to claim that he knows everything about Oliver and knows him better than he knows himself.
While trying to accomplish his mission, Adrian developed the facade of a compassionate district attorney who cared about cleaning up the streets of Star City and ironically a trusted confidant to his father's killer. In reality, Adrian's hatred for Oliver was so intense that he refused to allow anyone else to kill Oliver, as shown when he threatened and later killed Tobias Church. In spite of his hatred for Oliver, Adrian was not interested in killing him but to make him suffer so much that he wished that he was dead. Adrian had gone to great lengths to psychologically torture him and destroy his life including: killing innocent people to send a twisted message to Oliver, recreate the crime scene with dead bodies of Oliver's killing of Adrian's father, kidnapping his loved ones, and recruiting Black Siren, the Doppelgänger of Laurel Lance who Oliver loved. Adrian's hatred for Oliver even outweighed the apparent love that he had for his wife, Doris, as he killed her when Oliver used her against him and tearfully proclaimed she would go to the police.
Adrian also believed that Oliver was not a hero but a killer who ruins the lives of everyone that he comes into contact with and was desperate to show that to him. Going so far as to physically and psychologically torture Oliver for an entire week, Adrian succeeded in proving that on some level Oliver enjoyed killing. Adrian was also a hypocrite on some level as despite viewing Oliver as a killer he himself committed far more heinous actions than Oliver did, freely killing innocent people, using some of his victims' bodies as trails to recreate the scenes of Oliver's past kills, and even killing his own wife to further his vendetta, where Oliver never killed anyone who had not committed at least some kind of crime, proving that even though Oliver is a killer, Adrian is a psychopath. Adrian was also arrogant, smug and boastful towards Oliver and Team Arrow once they realized that he was "Prometheus" due to Adrian always being ahead of them and their inability to apprehend him at the time.
Adrian also had no personal disregard for his own life, as on several occasions he allowed Oliver the opportunity to kill him albeit at the cost of Oliver destroying his own life in the process. Adrian again allowed Oliver the opportunity to kill him but once he refused, Adrian forced Oliver into destroying his own life either by forcing Oliver to choose between his son or Team Arrow. Once Oliver succeeded in saving them both, Adrian, without hesitation, ended his own life to once again make Oliver suffer by losing virtually everyone else he cared about on Lian Yu.
- Expert archer: Like Oliver, Adrian was a trained archer although he seems to prefer throwing weapons. Adrian is skilled enough to either wound or kill his targets and use his bow as an improvised quarter-staff like Oliver. While torturing Oliver, Adrian fired three arrows in Oliver's chest in a tight pattern at point blank range.
- Computer specialist/Expert computer hacker: Adrian had demonstrated a high degree of computer skills, as he was able to build and use several theatrical traps which he used against Oliver and Team Arrow. Oliver also mentions that Adrian has managed to erase all traces of his birth identity as "Simon Morrison" from the internet.
- Expert lawyer: As a former District Attorney of Star City, Adrian was a skilled lawyer able use his legal knowledge to successfully prevent John Diggle's prison transfer. It is possible that Adrian did not even possess a law degree, making his knowledge potentially even more impressive. 
- Expert swordsman: Adrian was trained in the art of swordsmanship, often using his sword fighting skills in conjunction with his melee skills; his exact level as a swordsman was unknown.
- Free-running/Acrobatics: Adrian was able to move and scale down walls with great dexterity and grace, even while throwing his shurikens.
- High tolerance for pain: Adrian had a high tolerance for pain as he could keep fighting without slowing down after Evelyn cut his arm and barely flinched after being shot in the shoulder with a bullet and was still able to move his arm normally even when the wound reopened.
- Intimidation: Adrian possessed an intimidating presence due to his ruthlessness with Tobias Church, Evelyn Sharp, and even Laurel Lance, a meta-human, showing signs of fear towards him; his killings as the "Throwing Star Killer" combined with media rumors and his presence was enough to cause a city wide panic. Even Darren Coffman stated Adrian was terrifying.
- Master hand-to-hand combatant/Martial artist: Adrian, like Oliver, was an incredible martial artist trained by Talia al Ghul with fighting style incorporating several moves that Oliver knows. Adrian was able to defeat Evelyn Sharp, Curtis Holt, and Vigilante in single combat. During all his battles with Oliver, Adrian fought on par with him and even managed to outpace him in some of their encounters.
- Master interrogator/Torturer: Adrian was a highly skilled interrogator, trained in both verbal and physical extraction techniques. As a lawyer, Adrian was successfully able to flip one of Eric Dunn's men to find him. While torturing Oliver, Adrian tortured Oliver using same methods of Oliver used to kill his enemies; including water-boarding and shooting him with arrows all while not killing him. At the same time, Adrian psychologically tortured Oliver by threatening his loved ones and seemingly killing Evelyn in front of him. Adrian was eventually successful in breaking Oliver and convinced to end his crusade temporarily, due to the efforts of John Diggle.
- Master investigator: Adrian had proven himself to be a highly skilled investigator, having learned much about Oliver and all those close to him. Adrian is aware of their secret identities, the list, the S.T.A.R. Labs pipeline, the Legends, and the multiverse. Adrian was very skilled at locating people as he was able to find the elusive Talia al Ghul and William Clayton, despite his mother, Samantha's best efforts to keep him hidden and safe.
- Master marksman/Knife-thrower: Adrian was an incredibly skilled marksman who was highly proficient in throwing weapons such as knives, battle axes, flechettes and his weapon of choice; shuriken. He was able to disarm police lieutenant Conahan while jumping and was able to perfectly split an arrow shot at him by Oliver in half by throwing a shuriken. Adrian was a capable knife wielder as shown during a confrontation with Oliver.
- High-level intellect/Master tactician/Manipulator: Adrian was a highly effective tactician, with his tactics against Oliver being at a psychological level, as he was successful in tricking Oliver into killing Billy Malone; knowing that Oliver came with the intention on killing Adrian making the latter one of the few people to ever tactically outsmart Oliver who is a master tactician in his own right. Adrian was also very manipulative able to convince Evelyn to betray Oliver, and he positioned Oliver in a scenario where he was forced to proclaim his "Green Arrow" identity as a police killer making it nearly impossible for him to take Prometheus down with his alter ego.
- Peak of human physical condition: Adrian was in top physical form after training for four years to defeat Oliver. He was strong enough to pin down the large and physically imposing Church, and Earth Two Laurel, a meta-human, with one arm and kick Oliver through a wooden wall with one leg. He also had a high tolerance to drugs, as he was able to quickly shrug off the effect of the Diazepam-ridden dart that Oliver threw at him. He also withstood a severe beat down from Oliver which left his face bloody and swollen, and barely seemed fazed by it.
- Skilled metalsmith: Adrian has stolen several of Oliver's arrows that Oliver has left behind during his vigilante career and melted them down to be reforged as his own weapons; mainly his shuriken.
- Stealth/Infiltration: Adrian is highly skilled in the art of stealth, as he is able to sneak in or appear to people fairly quickly without them noticing. He was able to sneak into S.T.A.R. Labs without triggering any alarms, an act that went unknown to them for 3 days.
- Network: As a former district attorney, Adrian had access to the resources of his office and the Star City Police Department. Adrian was also apparently second-in-command of Talia al Ghul's cult, all whom where his fellow students.
- Prometheus suit: Adrian wears a protective suit as Prometheus, to hide his identity from his victims, in his quest of vengeance against Oliver Queen.
- Shurikens: Adrian carries Shurikens strapped to his abdomen, usually no more than six at a time. These appear to be his preferred method of killing his victims.
- Quiver: Adrian carries a black arrow container, to carry his arrows with him.
- Chokuto: Adrian carries a chokuto on his back for close quarters combat.
- Axe: Adrian carries at least one axe.
- Throwing knives: Adrian carries several smaller and easily concealable throwing knives.
- Voice filter: Adrian apparently uses a voice filter in his mask to conceal his true identity and making him sound almost unrecognizable as Prometheus. For some reason, he made several alterations to his disguised voice. This is possibly what he used to mimic Lyla Michael's voice to trick John Diggle.
- Pistol: Adrian used a pistol when taking William hostage. He then used it to kill himself after Oliver saved William.
- Adrian chose the name Prometheus, because Prometheus challenged the omnipotence of the gods, because Adrian believed that like Oliver, the gods played judge, jury, and executioner, but Prometheus took away the gods power.
Behind the scenes
- In the DC comics, Adrian Chase is known as the first Vigilante in present-day. In the series, Adrian is a separate character and an antagonist, while Vigilante is Vincent Sobel. Like on the show, Chase's insanity ultimately leads to him committing suicide.
- In DC comics, Prometheus is an alias used by multiple villains, most famously by an unnamed one that pushed Green Arrow past his limits. This version does resemble said character in looks and modus operandi, being a mass-murdering "dark mirror version" of the hero he opposes, skilled with several fighting styles and weapons. Another resemblance is that Prometheus' main motivation is to avenge the death of his criminal parent and will go to great lengths to do it, similar to the comics, where his parents were criminals killed by cops and because of it, he wants to destroy all forms of justice. Both claimed to be too smart for Green Arrow to overcome and made overly elaborate plans, but were subsequently proven wrong by Oliver and defeated, though they managed to cause massive explosions in places close to Oliver's heart. In the comics he destroyed Star City, and on the show he destroyed Lian Yu.
- He also has similarities to the Batman character Arkham Knight, an alias used by Jason Todd, the second Robin, in Rocksteady's Batman: Arkham Knight video game. Wrongly believing Batman abandoned him after Joker faked his death and tortured him for over a year, Jason swore revenge and adopted darker version of Batman's suit armed with more weapons, with the Arkham Knight alias to kill his former mentor. Adrian suffered a loss at Oliver's hands and uses a darker version of Oliver's suit with even more weapons than he carries as part of his vendetta against him.
- He also has similarities to Hunter Zolomon/Zoom. Both of them are the darker version of their respective enemies with similar backgrounds caused by the actions of their fathers. Black Siren worked with both of them, and both of them help their respective enemies while feigning friendships with them under fake names, and simultaneously opposing them in their evil personas.
- Interestingly enough, his alias mirrors him being the darker version of Oliver, since Adrian literally meaning "the dark one".
- The name 'Simon Morrison' is a reference to the original creator of Prometheus, Grant Morrison, with Simon being based off 'Simon Hurt', a Batman villain he created. The character Simon Hurt also shares several similarities with the show's Simon Morrison.
- Prometheus is the first main antagonist in the shared multiverse to willingly commit suicide (not counting Merlyn, as he wasn't planning on his daughter stepping on a mine). He is also one of the three main Arrow antagonists alongside Malcolm Merlyn and Slade Wilson to be credited as a main character and also have past history with Oliver. Additionally he was also the first main antagonist to be credited as a main character in his first appearance in the series.
- While he has a history with Oliver, Prometheus is the first antagonist with a history with Oliver that Oliver was unaware of in their first encounter, as it took several episodes for Oliver to learn of Chase's ties to his father.
- Prometheus is the fourth Arrow main antagonist to die. The first two that died in earlier seasons are Ra's al Ghul and Damien Darhk, and Malcolm Merlyn was the third, but he is not confirmed to be dead and is only presumed dead. However, Prometheus is the only one that has yet to appear on Legends of Tomorrow.