Lex Luthor (Arrowverse)

"Lena: Lex went insane. Lillian: Exactly. And if they could take the brightest mind on Earth and drive him crazy defending himself, imagine what they could do to you."

- Lena and Lillian Luthor arguing about Lex's madness.

Lex Luthor is a villain in the CW TV series, Supergirl. He is an unseen antagonist in the premiere of Season 2. He will appear in Season 4 in an unknown role. He is the former CEO of Luthor Corp (later L-Corp), the incarcerated archenemy of Superman and the half-brother of Lena Luthor.

He is set to be portrayed by Jon Cryer, who is best known for playing Alan Harper on Two and a Half Men.

Origins
Lex was born to Lionel and Lillian Luthor and hails from one of the most prestigious and wealthiest families in Metropolis. Even at a young age, he showed a high-level intellect which his mother saw him as a genius. After a four-year old Lena (secretly Lionel's illegitimate daughter) was adopted into the family, Lex made her feel welcome when they first met and played chess in which she eventually won.

Although he was apparently close with his sister during his childhood, he became more cold, power-hungry and delusional to the point of their relationship becoming estranged. Also, despite his close bond with his mother and half-sister, it is strongly suggested that he had a bad relationship with his father, who favored Lena more than him. Despite this, when Lionel died, Lex inherited the family company Luthor Corp. After this, he then hired Mercy Graves and her brother Otis as heads of his security. Lex's relationship with Mercy grew over time and eventually, she became his closest confidant and frequent dinner guest.

At some point, Lex became partners-in-crime with Bruno Mannheim for illegal schemes related to Luthor Corp. With Lex's help, Bruno laundered money through Luthor Corp, but he soon dumped Lex as his partner when the latter was investigated by the state. The center of the scheme were the parking lots, which Bruno purchased through a subsidiary he bought from Lex. According to Lena, it was Lex's relationship with Bruno that was the real reason that he was sent down the wrong path in his life.

Rivalry with Superman
At some point, Lex became best friends with the Kryptonian superhero Superman and the two initially tried to work together to repel the threat of alien invasions. However, Lex's methods were far crueler than Superman's, which set them at odds. Although the superhero tried hard to trust his friend, defending him against accusations of others and continuing to give him several chances to atone for his wrong deeds, Lex ultimately proved unable to forever deceive Superman, who eventually realized his true nature and this consequently resulted in a falling out between the pair. Shortly after this, Lex came to believe that Superman himself was the cause of alien terrorism since his presence attracted them and declared war on his former friend, becoming his greatest enemy. Lex's obsession of defeating Superman also soon dissolved his relationship with Mercy.

After he started targeting Superman, Lena grew concerned for his well being and tried to help him, but he ignored her and proceeded with his plans to destroy Superman committing unspeakable crimes in Metropolis, one of which was triggering a fault line in California with an "earthquake machine", which was tended to by the Kryptonian. Another incident involved Lex creating and selling a series of battle armors he called Lexosuits, which Superman was not happy about. Lex would use the suit in order to even the playing field when facing the Kryptonian. Over the years, Lex built many secret storage facilities around the world, where he keep various arsenals of weapons that he collected to defeat Superman once and for all. Lex also converted his own cloaked mansion's basement into a bunker facility designed to protect him from any threats and only confided in Lena of the mansion's location.

Eventually, after several years and various brutal encounters resulting in numerous fatalities, Lex was defeated by Superman, when the latter successfully exposes his crimes to the public and he was incarcerated for 37 consecutive life terms in Stryker's Island Penitentiary. Mercy was a key witness in the trial against Lex, betraying him as she had grown frustrated with Lex’s obsession on defeating Superman rather than looking at the bigger picture.

Post Incarceration
After Lex was sent to prison for his crimes, Lena took over the company and planned to rename it as L-Corp and cut off all ties from his name. Enraged by this, Lex hired the assassin John Corben to kill her. However, this plan was thwarted by Superman and his cousin Supergirl.

Even with Lex still in prison, his crimes forever tainted his family's name as nobody trusted a Luthor again. This is evidenced by his mother losing her medical license without even being granted a hearing, and when Lena was accused of breaking her out of prison, nobody began to trust her instantly due to being her daughter.

Eventually, thanks to Lena tricking Lillian, Lex's partnership with Bruno and his involvement in the latter's money laundering business was exposed to the public and under investigation.

Trivia

 * Luthor's previous friendship with Superman mirrors the same relationship his counterpart had with him in the Smallville series.
 * Although he hasn't yet physically appeared in the series (save for his flashback appearance), he is repeatedly referenced and mentioned by many heroes and villains, and he is best remembered for his crimes of terrorism against both human and alien life as well as his rivalry with Superman.