Alexander Joseph "Lex" Luthor () is a supervillain appearing in American comic books published by DC Comics. The character was created by Jerry Siegel and Joe Shuster. Lex Luthor originally appeared in Action Comics #23 (cover dated: April 1940). He has since endured as the archnemesis of the superhero Superman.

Lex Luthor was originally depicted as a narcissistic and egotistical mad scientist from the 1960s to the mid-1980s. Since the mid-late 1980s, he has more often been portrayed as the power-mad CEO of LexCorp. He wishes to rid the world of Superman, ostensibly because he views Superman as a threat to humanity, but in reality envies Superman's popularity and influence. Given his high profile as a supervillain, however, he has often come into conflict with Batman and other superheroes in the DC Universe. Lex Luthor is physically an ordinary human and has no natural superpowers, but has genius-level intelligence with a high aptitude for business and politics and a deep command of science and technology. He occasionally wears his Warsuit, a suit of mechanized armor that gives him enhanced strength, flight, advanced weaponry, and other capabilities. While Lex is primarily depicted as a supervillain allied with other villains in the likes of Metallo, Parasite and Bizarro, and frequently leading DC supervillain teams such as the Legion of Doom, he has also been portrayed as an antihero who will ally himself with Superman and other heroes when the situation calls for it.

The character was ranked 4th on IGN's list of the Top 100 Comic Book Villains of All Time and as the 8th Greatest Villain by Wizard on its 100 Greatest Villains of All Time list. Luthor is one of a few genre-crossing villains whose adventures take place "in a world in which the ordinary laws of nature are slightly suspended". Scott James Wells, Sherman Howard, John Shea, Michael Rosenbaum, Jon Cryer and Titus Welliver have portrayed the character in television series, while Lyle Talbot, Gene Hackman, Kevin Spacey, and Jesse Eisenberg have portrayed the character in films. Several actors have provided Luthor's voice in animated adaptations, including Clancy Brown, Mark Rolston, James Marsters, Giancarlo Esposito and Marc Maron.