Lex Luthor is a fictional character, a DC Comics supervillain and archenemy of Superman. Created by Jerry Siegel and Joe Shuster, Luthor first appeared in Action Comics #23 (1940). His history has been retconned several times since then, with his current canonical origin being Mark Waid's 2004 limited series Birthright.

The (usually) bald-headed Luthor has been Superman's main foe for most of the superhero's existence and has unveiled countless plots to destroy him and take over the world. Originally Luthor was a mad scientist but has since been rewritten as a Machiavellian industrialist and white-collar criminal. For a brief period in the early 2000s, he was president of the United States.

Luthor is one of several Superman characters with the initials "LL," including Lois Lane, Lana Lang, Lionel Luthor, Letitia Lerner, Lori Lemaris, and Linda Lee (aka Supergirl).

Luthor has been featured in most adaptations of Superman outside comic books. In the film series of the late 1970s and 1980s, Gene Hackman took a comical approach to the character. Stan Jones provided Luthor's voice in the 1970s and 1980s SuperFriends cartoon series. In the 2000s live-action series Smallville, a retelling of Superman's early years, a young adult Lex is played by Michael Rosenbaum. The role of Lex Luthor will be played by Kevin Spacey in the upcoming movie Superman Returns.