Supergirl season 4 will finally introduce The CW's version of Lex Luthor - but could he actually have been the show's villain all along? It's perhaps inevitable that Lex will become one of Supergirl's greatest threats - and he has a known grudge against her cousin - so he could have been manipulating events from the shadows ever since season 1.
It's always seemed to be only a matter of time until Supergirl introduced Lex Luthor, who has been talked about since season 1 aired in 2015. Luthor has been mentioned as a crazed supervillain who was apparently defeated by Kara's cousin, Superman. Driven insane by a lust for power and his hatred of aliens, Luthor was sentenced to 32 consecutive life sentences.
Supergirl season 4 has cast a new light upon Lex Luthor's imprisonment. It seems that his trusted chief of security, Mercy Graves, was like a member of family to the Luthors. Then, in a shocking twist, she betrayed Lex over a philosophical dispute and turned State evidence against him. This revelation took viewers rather by surprise; in every previous incarnation, whether in comics, TV shows, or even movies, Mercy Graves has been Lex's most loyal assistant. Even stranger, after Lex had been put behind bars Mercy was hired by his mother, Lillian. Why would Lillian, another shady anti-alien figure, hire a woman who'd betrayed her son? This suggests we should reinterpret everything we thought we knew about Lex Luthor in the Supergirl universe.
It's possible that Lex Luthor had himself deliberately placed behind bars. Imagine a scenario where Lex realized that his criminal enterprises were drawing too much attention. An easy way of dealing with this would be to be apparently defeated by Superman, betrayed by people he had trusted, and to go to prison. Secure in the knowledge that people would assume he was dealt with, he'd then be able to proceed with his plans without scrutiny. Notice that so many of Supergirl's greatest threats have been anti-alien groups, led by people Lex trusts or even with access to his technology. Lex could easily be the true mastermind behind Project Cadmus and the Children of Liberty, both serving as vehicles for his anti-alien agenda.
If that's the case, the Children of Liberty's unmasking of President Marsdin's true nature is a tremendous win for Lex Luthor. This is the moment when his cause goes mainstream, with a conspiracy theory proven and his acolytes able to argue that aliens had only been accepted because they'd successfully infiltrated even the highest levels of government. As a Durlan, Marsdin has been forced to step down as president, and her entire political agenda will collapse. The Alien Amnesty Act, in particular, is highly likely to be rescinded; it wouldn't be a surprise to see political pressure begin to push for an Alien Registration Act, a tool that would be perfect for use against Superman and Supergirl. Would they choose to register, revealing their secret identities, or would they instead become outlaws? Mercy's attack on the image inducers is just another strand to Lex's plan, another way of causing chaos.
Assuming this theory is correct, we're nearing Lex Luthor's endgame, so it's no surprise he's soon to step out of the shadows. One thing has always been true of every different version of Lex Luthor; he's always had an ego. If he's the mastermind behind everything Supergirl has suffered, he'll want Kara to know it.