Luthor is the principal antagonist of Superman. He first appeared in Action Comics #23 (April, 1940) by Jerry Siegel[?] and Joe Shuster. Although his history has been retconned many times since then, his current canonical origin is revealed in Man Of Steel #4 (August, 1986). He is one of several Superman characters with the initials "LL", including Lois Lane, Lana Lang, and Lori Lemaris[?] the Mermaid.
The original Luthor (who didn't have a first name) of the 1940s was one of many pulps-inspired mad scientists who plotted to take over the world, or destroy it, through the use of various diabolical schemes. He donned disguises a few times, but generally he preferred to make himself known to the world as his master plans came to fruition...until he was foiled, time and time again, by the Man of Steel. He soon became Superman's greatest foe, the antithesis of everything Superman stood for; and even though his plans for world domination were repeatedly dashed, he always managed to get away (or escape from prison) to threaten the world time and time again. Luthor was revealed to be the master villain in the second Superman serial, Superman vs. Atom Man[?], though he never appeared on the classic 1950s Adventures of Superman[?] TV series or in the original Paramount-Fleischer Superman cartoons.
Luthor's stated goals are to kill Superman, and to take over the world as a stepping stone to dominating the universe. Over the years, Luthor came up with every conceivable plan to destroy Superman; he has synthesized Kryptonite, travelled back in time, summoned beings from the Fourth Dimension, created robots, clones, and genetic monstrosities, allied himself with the alien super-computer Brainiac[?], animated Kryptonite rocks, detonated H-Bombs, and has masqueraded and taken on a number of aliases. During the 1980s Luthor adopted a powersuit that allowed him to battle Superman physically. Although none of his schemes worked permanently (though one classic "imaginary story" from the 1960s called The Death Of Superman has Luthor finally killing Superman with Kryptonite) Luthor's persistence has made him Superman's most troublesome foe.
Though originally portrayed with a full head of red hair, from 1941 onwards Luthor came to be portrayed as completely bald due to the mistake made by an artist who worked on the Superman daily comic strip. Shuster preferred drawing bald villains anyways, so the more striking bald appearance -- a Luthor trademark -- was thereby adopted. Several years later a back-story finally filled in how Luthor lost his hair, and that Luthor's hatred of Superman stemmed from a childhood incident where a teenaged Superboy used his superbreath to extinguish a fire that had broken out in Luthor's lab. Unfortunately for him, during this rescue attempt chemicals were spilled, causing Luthor to go prematurely bald and destroying Luthor's successful attempt to create new life through chemistry which might have also cured Superboy of his susceptibility to kryptonite. Luthor attributed Superboy's acts to jealousy on the Kryptonian's part and vowed revenge.
Though he was a noted villain and an evil mastermind on Earth, Luthor was revered as a hero on the alien world of Lexor where he utilized his scientific genius to rediscover the planet's technology and rebuilt society for the inhabitants. Superman himself has acknowledged that Luthor is a man of his word who would honor promises he made. Luthor had a younger blond-haired sister Lena Thorul[?] (her last name an anagram of Luthor) an empath who grew up unaware of her familial connection with the noted villain. Protective of his sister, Luthor had strived to hide his connection and had been assisted towards this end by both Supergirl and Superman.
In 1985, John Byrne's famous "re-boot" of Superman re-wrote the character of Lex Luthor from scratch, bringing him to the modern world and making him a villain that the 1980s would recognize: a corporate white-collar criminal. (The idea was originally suggested by Marv Wolfman[?].)
The current, "modern" history of Lex Luthor is as follows:
Born in the Suicide Slums district of Metropolis Luthor put a large insurance policy on his parents and had them killed by a car accident. Using this money and his natural genius he built a multi-national corporation for himself. He became the CEO of LexCorp International, based out of Metropolis. He was the most powerful man in Metropolis until Superman arrived. When terrorists attacked a society gala aboard his yacht shortly after his arrival, Luthor observed Superman in action and then tried to hire him as a bodyguard. But when Luthor admitted that he'd anticipated the attack but allowed it to occur in order to witness Superman first hand, Mayor Berkowitz deputized Superman to arrest Luthor for reckless endangerment. Luthor vowed to destroy Superman for this humiliation, and he has since devoted much time and energy to that goal; he is a man driven to be the best, having fought his way up from lowly beginnings by his own effort, and is resentful of how Superman was given his powers by random fate of birth. Superman survived every attempt but has never been able to prove Luthor's role in the attacks.
Luthor acquired the only sample of Kryptonite on Earth from the Kryptonite-powered cyborg Metallo[?], whom Lexcorp abducted just before Metallo succeeded in killing Superman. Fashioning a ring from the alien ore deadly to Superman Luthor began wearing it constantly to ward off his enemy. Unfortunately, Luthor suffered from a severe cancer in the 1990s, caused by the long-term radiation from his Kryptonite ring. Kryptonite exposure had not previously been thought to be harmful to non-Kryptonian life forms.
Luthor's hand had to be amputated to prevent the cancer's spread, but unfortunately by then it had already metastatized; it was eventually determined that the disease was terminal. Luthor faked his own death shortly afterward by taking his personally designed jet, the Lexwing on a proposed trip around the world and crashing it in some mountains, using this as cover for the transplant of his brain into a healthy clone of himself which he then passed off as his hithero unknown, illegitimate Australian son and heir. Later, when his new body also grew terminally ill due to the instability of the cloning process that was utilized, he had his brain again transplanted into a new cloned body that resumed the identity of the original Luthor.
Lex Luthor has cultivated a popular image as a great philanthropist; he has been instrumental in reverse-engineering alien technology for use in general consumer goods, upgrading Metropolis into a true "city of tomorrow," and when Gotham City was destroyed by an earthquake and then abandoned by the American government it was LexCorp that took up the massive task of rebuilding. He also played an instrumental role in assisting the Justice League in recharging the Sun during "The Final Night" crisis.
Lex became the 43rd president of the United States in 2000, winning the election on a platform of promoting technological progress (his first action as president was to take a proposed moratorium on fossil-based fuels to Congress in hopes of putting "a flying car in every garage"). He was assisted by the extreme unpopularity of the previous administration due to its mishandling of the Gotham City earthquake crisis; even given Luthor's tendency towards covert supervillainy, he could well prove to be a better choice for the office.
Luthor is currently widowed, having killed the mother of his infant daughter, Lena.
Actor Gene Hackman played the role of Lex Luthor in the 1978 movie Superman, and in two of its three sequels.
In the current television series Smallville, Lex is one of teenaged Clark Kent's closest friends. As a young boy, Lex was caught up in the explosion of baby Kal-el[?]'s rocket ship as it landed on Earth from Krypton. The explosion caused Lex to lose his hair. When Clark grew up, and was still learning how to deal with his super powers, he rescued Lex when Lex's car crashed through a bridge rail and went into the water. The two bonded, and Lex, living in Smallville as he runs his father's local business interests, considers Clark a "little brother". The depiction of the inevitable corruption of Lex and the development of his future enmity with Clark is a major plot arc of the series.