Early lifeLillian worked as a physician when she met billionaire Lionel Luthor, whom she married and gave birth to a son Lex. Sometime after their son was born, Lionel started having an affair and, when Lillian surprised him with his mistress on a business trip, wanting to rebuild things with his wife, Lionel sent his pregnant lover and paid her to keep quiet about the affair. Four years later, the woman died and Lionel decided to adopt his illegitimate daughter, Lena, despite Lillian's protests.
Over the next few years Lillian always favored her biological son over her adoptive daughter, as she considered Lex a genius and Lena not even a "real Luthor". However she claimed she did so just because Lionel felt guilty seeing his beloved wife together with the child born of his affair; though that's more likely a lie created by Lillian.
Leader of Cadmus
After Lex was sentenced to 37 life terms in prison, Lillian loses contact with Lena after Lex's trial. Infuriated by her son's imprisonment and the humiliation caused to her family by Superman, she took over Project Cadmus, a secret lab that studied aliens, and severed its relationship with the government so she could use it for her personal vendetta against aliens of all kinds.
When John Corben was shot by Lena and left near death, Lillian took him to Cadmus and, as he regained consciousness, she told him that she could kill him with one click but also make him survive, John agreed, and Lillian injected liquid kryptonite in his veins causing his eyes to cloud over. The woman says that now it will be called "Metallo". After Metallo woke up he was struck by his newfound power and asked the woman who she was, to which she replied: "merely a Doctor". She then introduced him to Cadmus and explained their anti-alien mission, which he hastily sympathized with. After that she gives him the mission to kill Superman and Supergirl. Later, despite the resistance of one of her subordinates, she ordered to turn him into another cyborg.
Lillian Luthor supplied whit alien weapon Chet Miner's gang to alarm public opinion, spreading fear and discontent over the population. The next evening Miner called the woman and told her that, as people are afraid of these weapons, he had fulfilled his part of the bargain and his next move would be to attack Lena Luthor's charity evening to make money. However, she warn him that if they attack Lena, she would not support them. After Miner is arrested he started to told Detective Maggie Sawyer who gave them the weapons but, suddenly, he heard Lillian's voice into his head, his ears began to bleed and he fell dead to the ground alongside the other two gang members.
Capturing Mon-El and SupergirlFew days later a bunch of Lillian's agents captures Mon-El and deliver him to an hidden base of Cadmus, putting him in a cage. Later, she told Supergirl at a special frequency that they have Mon-El and promised to kill him if she did not come. When Supergirl arrived in Cadmus, she met the real Hank Henshaw, revived as a cyborg, who was able to overcome her and imprison her in the cell next to that of Mon-El. Later Lillian revealed herself to Supergirl and threatened to kill Mon-El, if she does not deprive herself of solar energy with the help of a special device; Supergirl was forced to agree, then Lillian slapped her and took her blood before to sent her back to the cells, not bothering she and Mon-El later managed to escape thanks to Jeremiah Danvers.
After having sent Hank to stole a sample of the Medusa virus from the Fortress of Solitude, Lillian begins to release it to kill all the aliens in National City. Later Lena contacts her and says she want to join forces with her to release the deadly virus on Earth to wipe out all alien life. However, Lena had no intention of releasing the virus; she rendered it inert via a critical ingredient, and alerted the police about her mother's crimes. Lillian only realized she'd been double-crossed when the missile carrying the virus exploded sending only red rain falling on National City. Before she could react, the police swarmed in and arrested Lillian for attempted mass murder and other Cadmus-related crimes.
Freedom and ExodusLillian had her medical license revoked and her trial was impending. She received a visit from her daughter Lena and she told her that she forgave her for testifying against her though Lena told her that she wasn't buying it. Lillian then revealed that Lena was indeed a Luthor as Lionel was her father as he had an affair with her mother. She told Lena that the reason that they were always estranged was because her father didn't want her anywhere near her so she devoted her time to Lex instead. At her trial, Metallo managed to get a new Kryptonite heart which he used to free them both and draw Supergirl back and keep her from stopping them. When Lena was arrested for being a suspect in aiding in their escape, she sent Metallo to break her out of prison. Lena wasn't happy that she was broken out as it made her look guilty when she wasn't but Lillian told her that she had no where to go now. She told Lena that joining her and Cadmus was now her only option. They went to one of Lex's vaults where he had an anti-alien arsenal and that the only way to open it was with Luthor DNA, meaning Lena. Lena was angry with her as this was the real reason that they had broken her from prison but the vault was opened. Lillian was happy to see all of the things Lex had collected but was shocked to see that there was a mystery item there that Lex had completed. Supergirl arrived and Lillian had Metallo attack her though she tried to downplay her warnings that Metallo's new Kryptonite heart was unstable. However, when it seemed she was right, she and Hank Henshaw went and evacuated the bunker by a helicopter before Metallo exploded.
After having instructed Jeremiah Danvers to pretend to be rescued in order to infiltrate the D.E.O. and hand her the registration list of all the aliens living in the country, Lillian awaits him at a particular point and, after avoiding a vain attempt to capture by Supergirl and Alex Danvers, she travels with him and Henshaw in a secret facility of Cadmus from where they intended to launch their final plan.
Lillian had begun the next stage of Operation Exodus. They were rounding up all the Aliens that were registered in the country and were going to load them up into a space frigate that would jump into hyperspace and take all the aliens to a world all the way across the universe. Jeremiah told his daughter Alex that originally Lillian wanted to kill them all but he persuaded her to send them off instead. Lillian's mole that was posing as Lena's assistant warned her that her daughter was on to her so she ordered to have Lena halted. When Kara Danvers managed to post an article online that exposed their entire plan, she was forced to begin the launch early. Alex Danvers warned her that she had planted explosives all over the facility and would detonate them if she didn't halt the launch. At first, she thought Alex was bluffing until he detonated two of them. Lillian told her that she wouldn't stop it so Alex detonated them and then ran to stop the launch from the inside. Jeremiah then turned on her so she had Hank Henshaw take care of him before she fled. The plot was then foiled when Supergirl managed to keep the frigate from getting out of the atmosphere and making the hyperspace jump.
Lillian is shown to be very much like her son, Lex Luthor; cold, self-righteous, unstable and delusional in her views. Blaming Superman for her son's imprisonment, while completely in denial of the horrific actions Lex performed and his own choices, she has come to develop radically-driven disdain for aliens of all kinds. Viewing them as a poison to Earth, beings who are subtly taking control of the planet by making humans worship them, she is determined to purge Earth of these otherworldly-forms.
She is shown to be rather hypocritical, willing to kill bystanders, the very people who she claims to be trying to save, in her personal vendetta. While arrogant in her views and believing herself the true savior of the planet, Lillian is apparently a very shrewd and cunning woman. Able to anticipate how her enemies will act, she is able to plan several steps ahead and manipulate their actions.
Even outside her blind hatred of aliens, Lillian is shown to be very opinionated distant. During her entire adoption of her step-daughter, Lena Luthor, she made little effort in trying to connect with her new daughter, not completely agreeing with her husband's decision to adopt the child, preferring to focus her time on teaching Lex. Ultimately, she at most saw Lena as merely a good learning tool for her only blood-related child. Even in Lena's adulthood, Lillian's relationship with Lena was mostly professional, wanting to make sure Lena would keep the Luthor name in high regards.
However, Lillian's disdain for aliens greatly outweighed her strained relationship with Lena, determined to "protect" her from Supergirl and the likes. To which, Lillian's arrogant and selfish views also made her short-sighted. Between her eagerness to kill all aliens and people close to her living up to her high standards, it becomes much easier to deceive and manipulate her; when Lena apparently joined forces with her to release a deadly virus, she blindly let Lillian move about freely, allowing her to double-cross Lillian by sabotaging the virus and lead to her arrest.
Lillian is a liar, when she revealed to Lena that her husband is the latter's biological father, she claims that the reason why he never allowed her to form a close relationship with Lena, as he couldn't stand seeing Lillian together with the child born of his affair; however, in truth, Lillian has always been cold to Lena because she is a living reminder of Lionel's affair.
- Genius-level intellect/Expert scientist/Leader: As a scientist Lillian has a genius level intellect, as she was able to create cyborgs synthesizing kryptonite as a weapon and even to reproduce the Medusa virus from a sample.
- Indomitable will: A driven and determined person, Lillian is nearly fearless and almost always calm in every situation, as evidenced by not being intimidated even when menaced by a gang of men armed with alien technology or at the time of her arrest.
- In a grand sense of irony, Lillian is proven wrong about her opinions of Superman and Supergirl when it's Rhea attempts to conquer Earth.
Behind the scenes
- In the DC comics, Lex Luthor's mother is named Arlene Luthor. She debuted in Superman's Girlfriend, Lois Lane #23 (February, 1961) and was created by Jerry Siegel and Kurt Schaffenberger. In later incarnationsm her name was changed to Letitia, even though in most of her appearances she remains unnamed.
- The character was first given the name "Lillian" on the TV show, Smallville, on which she made her first live-action appearance.