- For the man he impersonated, see Hank Henshaw.
- "The more time I spend as Hank Henshaw, the less I have to face what I've lost. But when I change my state, shapeshift into someone new, call upon new powers, I get one step closer to becoming the Martian Manhunter forever. And he creates panic and hysteria. I know, I have seen it. It's not only that I'm better off as human. Everyone is."
- —J'onn J'onzz to Alex Danvers[src]
J'onn J'onzz (born 1699), commonly referred to as the "Martian Manhunter", is the last of the Green Martians. Born and raised on the planet Mars J'onn is the sole survivor of a "Martian Holocaust" instigated by the White Martians that also killed his entire family. J'onn fled to Earth and stayed hidden for centuries until he was discovered by D.E.O. Director Hank Henshaw. After Jeremiah Danvers sacrificed himself to save J'onn by killing Hank, the Martian began posing as director Henshaw to reform the D.E.O. for its intended purpose and became an ally of Kara Danvers/Supergirl's. Eventually J'onn finds himself forced to reveal his true identity and became a fugitive, however, after having helped to save the world from Non and Indigo assisting Supergirl in defeat them, J'onn received a full presidential pardon by Olivia Marsdin and was re-instated as director of the D.E.O., continuing to use Hank's appearance for convenience sake. Due to his identity being made public, as the "last Green Martian" J'onn is also one of the most wanted creatures to the eyes of the White Martians empire.
J'onn J'onzz was born in 1699 on the planet Mars, where he was raised. He hails from a peaceful race of psychic shape-shifters known as Green Martians and has lived a peaceful life with his wife M'yri'ah and his two daughters K'hym and T'ania. After he became a father, J'onn discovered his vocation for protecting the others and joined the Martian police. His idyllic life was cut short when the surface of their world was invaded by the White Martians, a subterranean race. They wiped out the Green Martians, including his wife and daughters, in the so called "Martian Holocaust".
J'onn however was somehow able to escape and wound up on Earth.
Arrival on Earth and discovery
After his arrival on Earth, J'onn spent centuries travelling the world and hiding from society, as his first attempts to make contact with humans created panic and hysteria; however at the end of 1800's he met a Shaolin monk with whom he made friend and from whom he learned meditation techniques.
At some point (approximately 300 years after his arrival), J'onn had at least one encounter with Earth's Kryptonian hero Superman, and whether or not this encounter ended up in a fight, it is still unknown, but it was enough for Superman to call J'onn "the most powerful being on Earth".In 2004, after being discovered on Earth, J’onn was tracked down in a remote location in Peru by the D.E.O. However, Jeremiah Danvers saved J’onn's life and stopped Hank Henshaw, with J’onn promising to watch over Alex Danvers thereafter. Disguising himself as Hank Henshaw, J’onn took over as the head of the D.E.O. reshaping it into a force of good.
Falling out with Superman
At some point afterward, J'onn meet with Superman again, and the latter helped him and the D.E.O. uncover an alien asteroid, composed of an emerald-green Kryptonian xenomineral. J'onn nicknamed it "Kryptonite" and resolved to store it in the D.E.O. as a contingency, which enraged Superman, thus leading to the pair falling out.
Head of the D.E.O.
The D.E.O. subdued Supergirl as she was mid-flight on her way to stop a fire. After she woke up at their base J'onn, as Hank Henshaw, introduced himself as the organization's director. After being released from kryptonite cuffs, J'onn explained to Kara how her ship brought Fort Rozz to Earth when it escaped the Phantom Zone, and released thousands of the galaxy's worst criminals. Afterwards, J'onn rejected her offer to capture them, telling her that if she wanted to help, she could go back to getting someone's coffee. Henshaw later sarcastically remarked on how Kara did in fact help, after she was defeated by Vartox and her wound opened up a possible way to ID his weapon, potentially giving the D.E.O. a way to defeat him. Later, Hank was convinced by Kara to let her intercept Vartox, after the satellites picked up on him heading towards National City, with him telling Kara, "Make sure you win." He was later questioned by Alex Danvers whether she was solely recruited based on Kara, with J'onn telling her that although that was the reason she was recruited, her own actions were the reason she got to stay.
A week later, J'onn along with the rest of the D.E.O. tested the limits of Kara's abilities, as he needed to know that she was in full control of her powers. The next day, J'onn questioned what Kara was doing at Plastino Chemicals during a D.E.O. investigation, though after the situation was explained to him by Alex, he told Kara not to touch anything. At the D.E.O. base, Kara told J'onn and Alex that the alien they were looking for was a Hellgrammite. J'onn was offered by Kara that the D.E.O. could track the Hellgrammite down, and Kara could defeat him, though J'onn came to the declined saying she could do so if she could prove to them that she could handle herself without being killed. The following day, J'onn along with Alex and Agent Hartmann came to the conclusion that the Hellgrammite was eating the DDT he had been stealing, as the government had been destroying remaining stockpiles, and his food source was shrinking. Later, the DEO set a trap for the Hellgrammite with a truck driving with tanks of DDT in it's back, and Alex and J'onn along with several other DEO agents followed behind it in another vehicle. Soon after Alex was abducted by the Hellgrammite, forcing J'onn to call Kara back the D.E.O. base. He was later berated by her for putting her through tests instead of trusting her, as the situation could have been prevented if she had been there. J'onn however reassured Kara that they had every satellite and a tactical drone searching for Alex. J'onn was later alerted to Alex's position after Kara discovered it through the use of her super hearing. Though he warned her to wait after she told him he that she was going to get Alex, he was ignored. J'onn later rescued both Alex and Kara from Astra, ordering the Kryptonian to halt. Though Astra grabbed J'onn by the neck, taunting that he had no weapon that could hurt her, he plunged a Kryptonite knife into her arm, prompting her to fly off. J'onn was later thanked by Alex for helping her setup the room in the D.E.O. base that Kara could talk with the AI that was found in her pod.
When Supergirl was attacked by a unmarked drone she took it to the D.E.O. headquarters, Hank revealed it’s not one of theirs. The drone was remarkably nimble, nearly evading Supergirl altogether before she managed to eye-beam it to an explosive demise. A drone with all the technologies of the company Lord Industries, a company founded by Maxwell Lord. General Sam Lane came to Hank and the D.E.O. to request help from Supergirl to test their new weapon the Red Tornado. In the aftermath of the battle, however, Supergirl had exhausted her solar energy through her heat vision and temporarily lost her abilities.
Revealing his secret to Alex and KaraHank assured Kara that her powers would return in a few days, meanwhile Alex was more suspicious than ever about Hank. In a holding cell an alien conqueror known as Jemm is determined to escape, but Hank informs the psychic criminal that the neural shielding can withstand his powers. Jemm threatens Hank's family, but Hank tells him that he has none. The earthquake also causes damage at the D.E.O., causing a power outage and a opportunity for Jemm to escape his cell. Hank and Alex seek out Alura for advice and gather a team to go after Jemm with psychic disruptor helmets. Believing he can trust Alex, Hank asked her to stay behind. When Hank does meet up with Jemm, he has already taken out his security guards, before Hank vanishes altogether. He returns and tells Alex that Jemm is using his power to control the security and fellow guards, and plans to stop him with a neural inhibitor. He wants Alex to remain at her post as well, but Alex decides it time to find out what Hank is trying to do behind her back. Jemm used his powers on Alex's partner and kills him just as Alex is tackled into a room by Hank, only to discover that Jemm plans to free the prisoners. Alex makes Hank handcuff himself to a wall, revealing she knows about his connection to her father's death, and wants Jemm to come to the control room. Jemm comes looking for Alex, who is ready with a gun and attacks him. However, he gains the upper hand and prepares to finish her off when he is suddenly attacked by Hank. Hank then turns on the lights and tells Alex that he’s truly not the enemy. Alex still demands answers, and he tells her that he's is not actually Hank Henshaw, explaining how he had died alongside her father when they were tracking a lost alien in Peru who was seeking refuge. Henshaw had wanted to kill the alien, but Jeremiah objected to such a cruel plan and died stopping him. He tells her that Danvers died a hero, and Alex realizes that Henshaw is the alien that her father saved and he reveals himself as a shape-shifter who copied Henshaw's appearance in order to reform the D.E.O. He then reveals himself as J'onn J'onzz, who is the last surviving member of the Martian race. He also tells Alex that he promised her father that he would look after her, hence, why he recruited her into the organization in order to keep an eye on her.
He tried to stop Kara from rushing in and facing Astra again, and Alex now knowing the truth about Hank, told her to trust him. When Astra was finally captured, Hank asked Alex about Kara revealing he is unable to read Astra's mind; Kryptonians are immune to his telepathy. However they figured out that Astra lost as a diversion, they confront Astra, just in time to inform them that Non and an army of Kryptonians are invading Lord Technologies. Hank using his powers to disable one of the Kryptonians' shields to weaken him after he found out Hank wasn't human. Kara suddenly arrives and is ready to battle Non.
After Hank was taken his secret emergency protocols reveal that Alex is his designated successor which helped in his search and rescue. Non killed a mind reading alien who found Hank impervious to his abilities. They then trade Astra for Hank and Astra upheld their truce. At CatCo, Hank used his shapeshifting ability to impersonate Supergirl so that Cat can see her and Kara at the same time. Cat accepted that she must have been wrong, and offers Kara her job back on the condition that she not reveal Cat's embarrassing mistake. Hank offered Kara a full-time job at the D.E.O., but she tells him that her relationships at CatCo are what humanizes her.
J'onn took Kara for a flying lesson to improve her aerial skills. Afterwards Alex convinced J'onn to use his powers to infiltrate Lord Technologies. Alex went on a date with Maxwell, giving J'onn time to sneak in and get the information. J'onn (posing as Maxwell) sneaks in and finds the mystery woman. When J'onn trips over the alarm a guard shows up but J'onn erases his memory and tells the woman he'll be back. When Maxwell returns, he discovers the guard has no memory of anything, including his own family.
Senator Miranda Crane had a rally about an anti-alien propaganda. Hank and the D.E.O. were there to witness any alien activity. A fast-moving white alien appears and attacked Alex and Hank raced to stop him but suddenly Hank's vision of what happened on Mars starts to come back and Alex saves him before he is run over. Alex also questioned Hank about why he froze, and he explained to both Alex and Kara that he knows the attacker: it's a White Martian, part of a subterranean race that wiped out dozens of his people on Mars, including his entire family. Hank wants to handle the attacker personally, but fears that if he reveals himself to the world, General Lane will try to take over the D.E.O. However, Kara tells J'onn she will help him. At D.E.O., "Miranda" plays mind games with Hank about an alien mole within the D.E.O. and threatens to out the D.E.O. if he doesn't conduct an investigation. When she suddenly mentions that she was attacked by a White Martian, Hank becomes suspicious. Kara tells Alex that the White Martian is at the D.E.O., disguised as Miranda. Alex arrives with a gun pointed at "Miranda" just as Hank goes for his weapon, but the White Martian is too quick for them. She goes on a rampage through the building. J'onn suddenly starts having visions of White Martians taking a race of Green Martians (who are children). Just as Miranda is about to attack, Kara shows up to challenge her only to have the White Martian escape.
Alex told J'onn that she felt bad for encouraging him for using his powers and shouldn't be at fault, but J'onn told Alex about how the White Martians killed his family before he escaped. He then noticed a tissue that came from "Miranda" and over Alex's concerns tracks "Miranda" down by hovering above the city using mind control, leading him to her lair located in a sewer. Posing as Hank, he bring Alex and the D.E.O. agents in to capture the White Martian, and stumble upon the real Miranda and rescue her, except for Alex, who becomes bait after the fake Crane captures her. J'onn then uses telepathy to negotiate with the White Martian while telling Kara to rescue Alex so he can kill her, which Kara objects to. The two arrive in the desert ready to come face to face with Miranda and pleads with her to let Alex go. J'onn is ready to surrender to the White Martian but Kara stops the alien and J'onn transforms into his Martian form and a battle ensues between all three. J'onn decided to take it further as he places Kryptonite cuffs on Kara so he can kill the White Martian, but Kara talks him out of it and he gives in. After they place the White Martian in the DEO cell, the alien vows there are millions like her ready to kill J'onn and won't rest until he's dead, but Kara tells her she's ready for them.
Hank and the D.E.O. witness Supergirl causing destruction, and figure out this must be the woman in Maxwell Lord's lab Hank and Alex formulates a plan to subdue Bizarro with Kryptonite which failed. The D.E.O. arrested Maxwell Lord and he helped create Blue Kryptonite which they are able to take her down and taken to the D.E.O. Hank said they are going to put her under, and Kara comforted her saying she went to sleep.
Kara is attacked by the Black Mercy putting her into a coma. Hank was annoyed that Alex also brought James and Winn to the D.E.O. They are unable to remove the plant and interrogate Maxwell Lord, but he knew nothing of it's origin. They tried to rip off the plant with a titanium claw, but this sent Kara into violent convulsions. Alex was forced to stop the extraction when Kara briefly flat-lined. They realized they cannot remove it by force without killing her. Cat Grant threatened to to fire Kara if she did not return to the office. Alex convinced J'onn to masquerade as Kara, but he had great difficulty fulfilling her difficulties. Astra informed Alex about the plant and wished to help Hank and Alex argue over whether to use virtual reality tech to free Kara. In the secret room at CatCo, J'onn brushed off inquiries of him shapeshifting into Kara, and was resistant to Alex's plan to enter Kara's mind due to its dangers. James and Winn were both concerned of what would happen to Kara after they pulled her out of her perfect fantasy. J'onn began to understand why Kara values them and allowed Alex to take them to D.E.O. while he dealt with Cat. At Cat's office, J'onn, once again in Kara's form, apologizes to Cat, and while he was unaware of Kara's fling with Adam, decided to roll with it. Cat didn't buy it one bit and acidly told "Kara" to take the day off. They sent Alex in to Kara's mind using VR technology and she was able to convince to leave the fantasy.
Taking the blame for Astra's death
Now free the D.E.O. went to stop the Kryptonians attack on their satellites. Alex killed Astra in battle using a Kryptonite sword. However Hank claimed that he stabbed Astra as he saw no other way. J'onn said that she never stopped hoping for Astra's redemption, and that's the difference between soldier and hero. Alex asked him why he lied about killing Astra, and he said it's because she's Kara's hero and he didn't want that to change.
After the death of Astra, Kara told J'onn they have two weeks. Alex told J'onn she could't lie to Kara about Astra's death any longer, but the latter insisted Alex was what Kara needed. Hank briefed D.E.O. agents about a Fort Rozz escapee who went by Gabriel Phillips. When they found him, he's been chained up and begged them to help him. An armored individual took the escapee Alex and Hank discuss the mysterious personality when Kara came in, asking why they didn't call her. When Hank said he thought she needed some time off, she bluntly retorted that she would request it if she needed it. During the investigation they learn the kidnapper is Fort Rozz; Master Jailer. He had taking it upon himself to execute the escapees. Supergirl is taken prisoner during a battle, but is rescued by the D.E.O. After the rescue Kara and she walked out, saying she didn't know how to work with him any more.
After Hank admitted to killing Astra, Kara refused to work with him. Alex and Hank spar and debate over whether Kara should know the truth, and Hank briefly reverted into his Martian form before changing back in an intense moment. He insisted that D.E.O. will continue to function without Kara and revealing the truth will only cause more pain, despite that he didn't want to lose her either. When Kara was attacked by Indigo at her apartment Hank and Alex arrived and drove her off. The D.E.O. and Kara and her friends work separately until she realized she needed Hanks help. Hank gave Kara the kill code to destroy a missile, shutting it off and allowing to plummet harmlessly into the ocean. Kara also returned to the D.E.O. and ready to work with Hank again. Alex came clean to Kara and admitted to killing Astra because she wanted to protect Hank, Kara forgave them both and reached out to hold Hank's hand.
Miranda Crane came to the D.E.O. to personally congratulate Hank, Alex and Kara for their efforts to fight alien threats. Unbeknownst to Hank Kara is exposed to Red Kryptonite on a mission altering her personality. He sent her on a mission to capture a K'hund who was robbing banks. However Kara let him escape, and when Hank discovered the truth they confronted her. She berated Hank for hiding his identity. They investigated her past missions and learned from Maxwell Lord about the Red Kryptonite. They now have a cure and Hank and a team went to stop Kara. However she was unstoppable and Hank was forced to take his true Martian form and engaged Kara, distracting her long enough for Alex to fire the antidote. Hank is taken into custody. Hank told Senator Crane that he is J'onn J'onzz. Crane felt betrayed and walked out. Alex wondered why J'onn didn't run, but J'onn said he would do anything to keep Alex and Kara safe.
Colonel Jim Harper was brought in to deal with J'onn infiltration of the D.E.O.. Jim along with Lucy Lane were there to clean up the agency. The two take J'onn still in the form of Hank Henshaw to a interrogation room that is so alien proof that Supergirl could not listen in. During the interrogation J'onn told the two about what happened ten years earlier in Peru, when he befriended Jeremiah Danvers. However, Jim, who was close friends with Hank, doesn't believe him and is placed in custody was plans to take him to Project Cadmus. After a moment of clarity, Lucy agreed to help Kara. Later that night, as the vehicle is en route, they are surrounded by motorcycles that throw the truck off course. One of the cyclists is Supergirl, who disarms the guards, while the other cyclist, Lucy, help Alex and J'onn escape, but not before J'onn erases Harper's memory of having remembered meeting him, but discovers that Harper now remember that Danvers is alive at Cadmus.
Alex and J'onn, posing as mother and son so they can elude authorities, arrive at Eliza's home, where after a moment to calm her down (as J'onn transformed to prove he wasn't Hank), reveal the truth about Jeremiah being alive. Eliza then informs the two about National City under quarantine and turns on the television. After a conversation over what happened and looking at pictures of Jeremiah and his daughters, J'onn gains the trust of Eliza and promises to keep a eye on Kara and Alex. Alex then gets a call from Kara, who asks about Project Cadmus, but Alex wants to return to National City to help. Kara, on the other hand, hangs up on Alex, warning her not to come or she'll be under Myriad. J'onn, however, agrees with Kara, and since he is not affected by Myriad, tells Alex to stay behind while he goes back to National City because her father still needs her, but later on and without explaining this to Eliza, both Alex and J'onn return to National City. When they return, Indigo is ready and waiting for the twosome as they're lured into a battle, with J'onn almost gaining the upper hand. Indigo managed to come back and attack J'onn and grabbing Alex. Indigo then orders a weakened J'onn to stand down or she'll kill Alex, and he does that, only to collapse, as Indigo is convinced that J'onn, being the last surviving Green Martian, has died.
J'onn survived and managed to heal in time to fly to Fort Rozz with Supergirl to stop Indigo and Non from overusing Myriad to kill all humans. While Supergirl and Non faced off, J'onn took on Indigo once again, but this time, he came out victorious and used his super strength to rip Indigo in half, an attack the robotic alien could not recover from. After Supergirl got rid of Fort Rozz and saved the world, J'onn, as Hank, celebrated along with Kara's other friends and family in her apartment. The celebration was cut short by the arrival of a third Kryptonian pod, which Supergirl and J'onn, back in his true form, went to check out. J'onn stood by as Kara looked inside the pod, shocked at learning about the inhabitant.
When Superman flew to National City, Kara took him to the D.E.O. to show him the man they had found into the pod the last night. Clark and J'onn has a strained relationship since the latter choose to keep Kryptonite at the D.E.O. as a precautionary measure. Despite the martian tried to talk with Superman on the advice of Alex, he claim they have nothing to say to each other, as he feels he can't trust him since, although he knew J'onn would not allow the Kryptonite in his possession to be used to kill him or Kara, Clark also knew that an order may come from above.
Once Metallo shows up in the city and almost killed Kara, as his body was composed partly of Kryptonite, Clark blames J'onn, who said that only D.E.O. have access to the Kryptonite, but a sample of their stock was stolen four months ago and they could not find it. Superman and J'onn went together to the Fortress of Solitude to find information about the metal that compose the cyborg's body so that Winn can make an Anti-Kryptonite Devices of said metal for Clark and Kara. After that, while Supergirl and Alex fought with Corben in National City, Superman and the Martian Manhunter dealt with a second Metallo in Metropolis and together were able to overcome him. In the evening of the same day, at the D.E.O., J'onn gave Clark the entire stock of Kryptonite in his possession sealed in lead. Clark said goodbye to everyone and flew back to Metropolis, taking the Kryptonite with him.
Meeting with M'gann M'orzz
After a while, Detective Maggie Sawyer showed Alex a bar frequented by aliens. J'onn got there in his Green Martian's guise and went to the bartender to ask for a drink, the woman was startled by his appearance and quickly left telling him her shift ended; J'onn however confronted her outside the bar where she took the form of a Green Martian claiming that her name is M'gann M'orzz, the last daughter of Mars. Later J'onn came again to the bar and asked to M'gann how she managed to escape from Mars during the holocaust. She said that she was taken to a concentration camp along with other Green Martians, and one day a good willed female White Martian disobeyed the order to kill the prisoners, and then helped her escape. Thereafter J'onn proposed her to establish a mental link to share consciousness, but M'gann refused. He later told Kara and Alex about his meeting with M'gann and that he offered her a mental connection saying that, in his opinion, it was a mistake. Later that day, Kara and Alex told J'onn they have seen M'gann in an underground fight club hosted by Roulette, in which the aliens are forced to fight to the death for the money. J'onn went to confront her about it but she claim it was her own business, to which J'onn replied that they should preserve what they have lost, and M'gann says that she wants to forget about everything. Before J'onn left, M'gann reveals him Roulette's real name and asked not to come to her.
The next day J'onn came to the alien bar to apologize M'gann, but they are kidnapped by Roulette's guards and forced to fight to the death for the title of "last Green Martian". Despite M'gann's attacks, J'onn refuses to defend himself and told her that she should not become a murderer just because she feels guilty for having survived all their people. After hearing this, M'gann stops the fight and says Roulette she will not kill him, so the ringmaster released Draaga to terminate them both but they are joined in the fight by Supergirl, who managed to defeat the enemy. Later J'onn comes to M'gann's home again and said that it was right they leave the past behind and that if she does not want to establish a connection, he will not insist. Before leaving he also adds that he'll always be there if she needs help.
Discovering M'gann's secretAfter Winn and Alex showed him a video of the Thorul Arctic Research Station in Norway, in which one of the scientists asks for help, J'onn and Alex go there only to find all the scientists were dead except for Rudy Jones, whom they brought back to National City. Later, however, the D.E.O. found out that it was Dr. Jones the one who killed all the scientists because he became infected by an alien parasite so J'onn and Supergirl confront the creature, who defeat them simultaneously sucking the life forces of them both. Despite Kara quickly recovers thank to solar radiators, to save J'onn's life, Alex decides to seek help from M'gann who was brought to the D.E.O. and informed that J'onn need a blood transfusion. Although initially she did not want to do that, M'gann agrees and saves his life. When J'onn wakes up, he sees M'gann sitting next to him, and thanks her for saving his life, asking her to stay with him until he falls asleep again.
The next day M'gann visits J'onn to assure his wellbeing and brings him a special martian recipe known as K'rkzar tonic, that he loved because his grandmother always gave it to him when he was a child whenever he was ill. Soon after, however, J'onn start to experience hand tremors and vivid hallucinations of his dead family or White Martian, so he asks Alex to do some medical tests on him and. After seeing the result of his blood test, J'onn deduces M'gann is actually a White Martian and confronts her out of the alien bar. M'gann tries to explain she's not like the others of her kind but J'onn believes she is just a liar and begin fighting her, beating her up almost to death until she assumes her human appearance begging him not to be killed in her real form, which prompts him to decide instead to incarcerate her at the D.E.O. National City headquarters, where she revealed to him that her blood is slowly yet inexorably turning him into a White Martian.
Medusa virusWhen Cadmus begins to release the Medusa virus to kill all the aliens in National City, as a precaution J'onn orders Kara to stay in the D.E.O. headquarters alongside him and Mon-El. After they realize that the virus is from Krypton and was created by Kara's father Zor-El, J'onn tries to comfort her as she reminiscing of her life on Krypton, admitting that her parents were not who they seemed. Suddenly, J'onn was struck by an immense wave of pain, showing his oncoming White Martian form and explained what had happened with M'gann's blood transfusion, believing there to be no cure. Later on, J'onn and Supergirl left to the National City port, where Cadmus planned to release Medusa via air; while Kara went after the rocket with the virus J'onn took on Cyborg Superman transforming completely into a white martian but keeping control of himself. When the virus is spread, J'onn stops fighting and prepare serenely to meet death and rejoin his family, however thanks to Lena Luthor's betrayal against her mother, the virus is made inert, with no risk to any alien, and the leader of Cadmus is finally arrested. Later, thanks to Eliza Danvers's reverse engineering of a living sample of the virus, J'onn's blood is drained from all the White Martian's blood cells, returning to his normal Green Martian form.
After M'gann suffered a telekenetic attack from the White Martians that left her in a catatonic state and started to slowly die, J'onn was hesitant about helping her because of his old hatred for her kind, however, he decided to save her life through the Martian Bond. J'onn went into her mind where he found M'gann in a memory of her time at the Galle Crater's internment camp. M'gann told him that she was ordered to kill a Green Martian boy but she refused turning on the guards instead and that she pretended to be a Green in order to help J'onn feel less alone to try to atone for what she did. J'onn assured her that she didn't have to feel so guilty anymore, he managed to pull her out of her coma but she told him that the White Martians will be coming for her now.
Under the disguise of Hank Henshaw, J'onn appeared cold and calculating, believing that Kara using her powers would only add to the public unrest caused by her cousin's heroics. After he revealed his true identity to Alex and Kara respectively, J'onn is actually kind, caring, selfless, intelligent, has a sense of justice, honor and good morals. He does also have a very sharp wit and has been shown to care for Alex and Kara as if they were his own daughters to the point when Clark accused him of not caring for Kara's well-being, J'onn lashed out telling Clark to watch his mouth.
Normally, he is very calm, level-headed and patient, as he rarely loses his temper, however, he has no tolerance for those who disrespect his comrades. J'onn is also cold towards people that he dislikes for good reasons; like Sam Lane, due to the latter's arrogant, rude, disrespectful, ungrateful, selfish and immoral traits.
J'onn was initially very reluctant to use his powers, as he believes people will get hurt if he does use them. However, after his identity as the Martian Manhunter was revealed to the D.E.O., he gradually become more confident of his ability and alien heritage and starts to use his powers more frequently.
There is a dark side of his personality; as J'onn can be cold, cruel, ruthless and vengeful, this is evidenced by the fact when he comes face-to-face with a White Martian, he would have killed the latter, if Kara and Alex and not convinced him to spare its life. J'onn has a deep hatred for the White Martians due to the fact that they wiped out his entire race, and killed his entire family for no apparent reason; simply to indulge their own warmongering desires. This made it hard for J'onn to accept that not all White Martians, like M'gann M'orzz are evil.
J'onn is cautious but at the same time short-sighted, as he resolved to store Kryptonite in the D.E.O. as a contingency, to safeguard against potentially rogue Kryptonians, thus leading to a falling out between him and Superman, who believed that the Kryptonite the D.E.O. had could fall in the wrong hands, and be eventually used against him or his cousin Kara, a fact J'onn did not consider. This fear of his proved to be correct, though the situation was resolved when all the D.E.O.'s Kryptonite was entrusted to him.
Despite being an alien himself and wanting the planet Earth to be a safe place where humans and aliens alike can live in peace, J'onn is a hypocrite and has problems trust other aliens, when president Olivia Marsdin was planning to initiate the alien amnesty act, a decree on granting aliens the rights of US citizens, he was unsure about it, claiming that some aliens would take advantage of Olivia's goodwill; however, the latter put J'onn in his place, reminding him that the same thing was once said about him, when his identity as "Martian Manhunter" was revealed to the D.E.O., as J'onn was being hypocritical.
Powers and abilities
- Green Martian physiology: Like all Green Martians, J'onn possesses several incredible powers. Overall, J'onn is an extremely powerful being with even Superman referring to him as "the most powerful being on Earth".
- Camouflage: J'onn can blend within the environment by changing the appearance of his form to bend the light waves around him to match with his surroundings making him almost - but not completely invisible.
- Density-Shifting/Intangibility: As a Green Martian, J'onn is able to move through solid objects (such as walls and doors) or to increase his density to become near-invulnerable. He is shown to be able to use this offensively, allowing him to phase through people to cause internal damage or even pull organs out of the body, as he did to Metallo to remove his green Kryptonite infused heart. 
- Invulnerability: J'onn's body is far denser than a human's, but not quite as durable as that of a Kryptonian like Superman, while he is able to make himself more dense. As a Green Martian J'onn is immune to human diseases and illnesses.
- Longevity: J'onn's life span is considerably longer than a normal human and likewise ages much slower. Despite being over 300 years old, his health, performance, and natural appearance has remained unchanged.
- Shapeshifting: J'onn is able to change his form at will, even on a cellular level, completely altering his physical appearance, allowing him to transform or mimic other people or animals and other creatures. His abilities allowed him to appear with clothing and other wearable items when transformed and retain what he was wearing when in a specific form, such as his Martian Manhunter uniform or the sidearm he uses as Hank Henshaw. However, due to the fact that he was retaining his powers, he couldn't pass the biometrics scan locking mechanism that required Maxwell Lord's finger prints in order to access through. Also, when posing as Kara, he had trouble walking due the high heel shoes he had in that form. 
- Malleability: J'onn can stretch and bend his body and limbs. (E.g. into large whips to grab things at great distance).
- Accelerated healing factor: Due to his shapeshifting powers, J'onn is able to heal faster than a human would. This caused any wound inflicted on him to glow red and then vanish in minutes, which happened when he was shot with Hank Henshaw's special bullets. He was also able to heal himself soon after being stabbed by Indigo, though it took time for him to recover from it. 
- Super strength: J'onn has strength above that of a normal human, as well as aliens like Jemm, although not as strong as a fully-powered Kryptonian. He is able to augment his physical strength by focusing his telekinesis and using it in a tactile way. As shown when fighting a Red Kryptonite-infected Kara, J'onn is able to apparently surpass a Kryptonian's strength when using all of his powers (strength and telekinesis combined); however, it should be noted in his confrontation against Astra, even when J'onn used all of his powers, he was able to put up a fight, but was still ultimately no match for the latter. This is likely because unlike Kara, Astra had full control over all her powers.
- Telepathy: J'onn is able to read the minds of other people (except for Kryptonians), communicate with others mentally and projects his thoughts in to others, as well as hear others people's conversation psychically. His telepathic powers are shown to be very potent, able to overwhelm the minds of other powerful telepaths.
- Mental detection: J'onn can feel and detect the mind of others, as well as their intentions, emotions and mental states. J'onn use this abilities multiple times, as when he sensed Alex Danvers' presence at the D.E.O, knowing Jemm was controlling the mind of the guard the and when he track and detect the location of the White Martian. He can use this to see with his mind like a mental view.
- Mental Shield: J'onn can telepathically shield himself and others from mental intrusions with enough effort, such as preventing other telepaths from scanning his mind. Doing this for Alex Danvers caused him some discomfort due to the effort and was unable to sustain it when he was wounded. 
- Mind control: J'onn can control the thoughts and actions of others (except for Kryptonians), implant words in other's mind, as well as to erase or restore and alter the memory of others, reprogram other people's minds and put others to sleep or temporarily paralyze others. He was able to induce amnesia to a Lord Technologies's guard.
- Psionic Blasts: J'onn can project a powerful "Mental blast" than can hit the target mentally or leave them unconscious.
- Psychic illusion: J'onn can project realistic illusions in other people's minds and make them experience things that not actually happen.
- Psychic translation: As a Green Martian, J'onn can psychically translate other languages.
- Telekinesis: J'onn can move and manipulate multiple objects with his mind. He can also generate telekinetic shield and shock-waves. J'onn was able to shove, grapple and pull Jemm without touching him and while being several feet away, as well as seemingly make a metal grate fall from the ceiling into Jemm's path to separate him from Alex. several feet away.
- Flight: J'onn can use the telekinesis to move himself, and simulate flight. When flying he is able to easily keep up with Supergirl, who can go over Mach 3.3 and keep up with the Flash (who was able to move at Mach 3.3 at the time) while teaching her proper flight tactics in battle, although he is notably slower than Supergirl and the Flash.
- Shock-Waves: J'onn is able to project waves of telekinetic force to hit, propel, crush or cut a target.
- Telekinetic-Shields: J'onn is able to generate a shield of telekinetic force for different purposes (such as to block or deflect incoming attacks, or to contain a target).
- Expert driver/Pilot: J'onn is an extremely skilled pilot, being able to driving a vehicle while simultaneously shoot.
- Expert hand-to-hand combatant: As the director of the D.E.O., J'onn is an expert in unarmed combat, although he was not quite on par with Astra, who managed to defeat him in their brief duel.
- Expert stick fighter: J'onn is a capable stick fighter; he was able to go toe-to-toe with Lar Gand, an expert stick fighter in his own right.
- Master marksman/Firearms: As the director of the D.E.O., J'onn is an expert with firearms, as shown when he was able to shoot at the Hellgrammite while simultaneously driving a vehicle.
- Genius-level intellect/Expert tactician: Because of his extended Green Martian lifespan of over 300 years, J'onn is exceptionally intelligent, being an expert tactician, and being able to synthesize a special new variety of Kryptonite just for Bizarro.
- Multilingual: As a native Martian J'onn speaks that language fluently, in addition to English and Kryptonese.
- Pyrophobia: After seeing his people burn, J'onn developed a fear towards fire.
- Fire: While shape-shifting, any part of his body that comes close enough to touch fire partially transforms back into its true form, which could be used to expose him and even weaken him
- Hank Henshaw's bullets: The original Hank Henshaw designed bullets to be able to harm and weaken J'onn, causing glowing red wounds in his skin. Though, due to his regenerative healing abilities, they disappeared in minutes, which also undid the damage to his uniform. He would have been killed with these during his first encounter with Hank if Jeremiah Danvers had not saved him.
- Maaldorian atmosphere: The air of Maaldoria contains a special silicate which makes it toxic for Martians.
- Stasis-field device: When interrogated by Jim Harper, a device created by Project Cadmus was used to keep him from shapeshifting or using his other powers, which was specifically used to keep him in the form of Hawk Henshaw and render him effectively human. The device created a smell of burnt rubber, possibly working off his weakness towards fire and extreme heat.
- White Martian blood: If a White Martian's blood is injected into J'onn's blood system, it will slowly cause his original form to become that of a White Martian, turning into a White Martian with green skin at first. Along with hand tremors, he will start partially transform into a White Martian even when in his human form and will lose control of his ability to shape-shift. The infection can also affect his mind, as he hallucinated his dead family and saw a co-worker as one of the White Martians, which he nearly attacked.
Adventures of Supergirl
- According to Superman, J'onn is "the most powerful being on Earth".
- J'onn is 317 years old. According to Hank Henshaw he has lived on Earth for over 50 years as of 2005, however J'onn himself has claimed to have been on Earth for centuries, at least since the end of 1800's.
- J'onn's favorite food is Chocos, a DC Comics substitute for Oreos.
- Unlike the comics, J'onn's size in his true Martian form is much greater to that of a human, at least in his first appearance.
- When transforming his body, phasing through objects, or even when being wounded, J'onn's body gives off a red glow over its surface.
- J'onn was the one who came up with the name "Kryptonite".
Behind the scenes
- J'onn J'onzz debuted in Detective Comics #225 (November 1955) as the last survivor of Mars. Created by Joseph Samachson and Joe Certa, J'onzz became the superhero known as the Martian Manhunter.
- Even though the storyline of the Green Martian race being eradicated to the brink of extinction, leaving J'onn J'onzz the last survivor, is very popular through the character's lengthy publication history; in the DC comics, not all versions of J'onn J'onzz are presented as such.
- This is the third live action appearance of J'onn J'onzz. He previously appeared in Justice League of America TV-pilot, and the TV series, Smallville.
- Even though initially in the comics, J'onn's human form was that of a Caucasian man (detective John Jones), through the years, the character started to be traditionally depicted as an African-American man, while being in his human form. In his latest incarnation, one of the several personalities of J'onn, that are created by him, is that of FBI agent, Daryl Wessel, an African-American man. In Supergirl, David Harewood is the seventh actor, who is a man of color, to either physically portray or voice the character.