Supergirl’s Luthors are the first family of Arrowverse villainy and Lillian Luthor will be the most dangerous Luthor of them all. Since Lena Luthor first arrived in National City on an ill-fated quest to build an identity beyond her infamous last name, the show has relished following the drama and entanglements of the Luthor family tree. The inevitable arrival of Lena’s iconically more notorious brother, Lex, came close to sweeping Supergirl and her story almost completely off the game board. Yet, perhaps the most dangerous Luthor all along was the one with nothing to prove, who proved time and again to be the show’s most successful mastermind of nefarious schemes, the Luthor matriarch, Lillian.
Lillian arrived in Supergirl’s second season as the head of Cadmus, the secret organization determined to rid the world of aliens. During her tenure, Lillian accomplished impressive feats, including capturing Supergirl to acquire a blood sample that would grant access to the Fortress of Solitude and a deadly Kryptonian virus. She broke her daughter out of jail, not to rescue her, but to use Lena's DNA to access Lex's weapons vault. Lillian was an expert in exploiting her adversaries’ vulnerabilities, like bringing back the presumed dead Jeremiah Danvers. Even when faced with setbacks, Lillian profited, gaining additional resources, knowledge, and advantages over her opponents. She was instrumental in developing a method to counteract human use of the Kryptonian drug Harun-El in season 4. After Crisis on Infinite Earths in season 5, she once again emerged on top, calling herself an upgraded Lillian, having taken the camouflage of her power to the next level. Lex realized that partnering with this Lillian may be his riskiest undertaking.
Lillian Luthor, on any Earth, is more of a threat than her children primarily because she doesn't announce her intentions to the world. Her true agenda, the ongoing acquisition of power for herself, never falls prey to her ego and emotions, weaknesses she believes have led Lex and Lena into failure time and again. Lillian operates from the shadows, with little fanfare, as only the truly dangerous do. While her progeny haven’t inherited her poker face, Lex and Lena Luthor are truly products of Lillian’s creation; her most cherished projects.
When corrupt CEO Morgan Edge threatened Lena in season 3, Lillian revealed herself to be a fierce protector. While leading the mission to rescue Lena from the invading Daxamite ship, she used the mission as an opportunity to try and get rid of Supergirl. Lex and Lena always turn to their mother when they encounter physical and emotional roadblocks. When faced with scientific puzzles she can’t solve, Lena seeks out her mother. Lillian is always waiting in the wings to tidy up after her children are done playing at being villains and heroes, such as when she intervened with Lex’s dispersal device to solve the Daxamite invasion Lena unwittingly aided. Lex Luthor almost immediately sought Earth-Prime Lillian’s advice and she eagerly helped her son manipulate his sister into joining forces. No one is more skilled at manipulation than Lillian, and her most frequently used game pieces are her own children.
Earth-Prime reintroduced Supergirl’s calmest, most quietly sinister iteration of Lillian Luthor yet. She tells Lex that the Luthors of this Earth are revered, a status she won’t see upended, a warning that carries the tone of a threat. Lex Luthor may be considered the biggest Supergirl villain in the Arrowverse, but Lillian’s grasp of the big picture and long game that surpasses Lex’s capabilities makes her far more dangerous. Whatever her goals on Supergirl, Lillian has demonstrated she will do what is necessary to achieve them, bringing her children along for the ride as collaborators or pawns. Lurking behind the scenes of Supergirl with laser-focused dedication, unhampered by the need for validation that she has instilled in her children, Lillian is the Luthor to fear.