well, Lex Luthor is different with every interpretation. in the comics he originated as sort of mad scientist, building robots and such, causing mass destruction, etc. Prior to "Superman: The Movie", Luthor had always been pretty 2-dimensional, a typical comic book villain at the time.
The Gene Hackman portrayal in the earlier Superman films gave Luthor a bit more character, and made him witty and a bit comical, with an air of "nobody's cleverer than me, i'm the greatest criminal mind of all time". That Luthor also wasn't bent on "world conquest", but on real estate, very expensive real estate. His goal in all the films (minus Superman III, which he isn't in, and Superman IV, where he has a different agenda: revenge) usually delt with him trying to get expensive land for himself: Superman I, buy up all the desert land in California, launch a nuclear missle at the San Andreas Fault, thus destroying the west coast and by effect make his desert land the only land worth living on; Superman II, help the 3 Kryptonian villains obtain Superman in exchange for possesion of Australia; Superman Returns, use stolen Kryptonian technology to create a new continent that he would own.
After the Crisis On Infinite Earths in the mid 80s, the Superman series, as well as sum others, i think, was revised and revamped. In other words, started over. Lex Luthor was now a more cunning, more sinister mad scientist. However, this Luthor didn't last long. After crafting a kryptonite ring to wear in order to keep Superman away, radiation from the ring eventually gave him cancer. had to amputate his own hand. in order to survive, he faked his own death in a plane crash, then had scientists take his brain and create a clone body around it. through this clone body, he pretended to be his own son, australian-born Lex Luthor II, and to the public, pretended to be a very good and generous businessman as a cover-up for his dastardly deeds.
the Lex Luthor II idea was played upon in Superman: The Animated Series. Here, Luthor is a very sucessful businessman, the richest and most powerful (next to Superman, and different sense of the word) man in Metropolis, very calm and refined. He's like Metropolis's architect, he's built half the city or so. To the public, he's a great man, but he sercretly does bad things like creating weapons for enemy countries or, of course, trying to kill Superman. the only people who don't trust Luthor are Superman, who knows how bad he is but has no way of proving it, and Lois, who thinks he's scum (in the 2nd ep, it's meantioned Lois and Lex used to date). Later, in Justice League and Justice League Unlimited, Luthor evolved into a greater threat by joining with other villains and creating much more trouble than he ever caused in Superman: The Animated Series.
In Superman Returns, Luthor's now played by Kevin Spacy, but since the move is more or less a "sequel" to Superman I and II, it's the same Luthor as Gene Hackman's Luthor. However, Spacy has said that he did his best not to look upon Hackman's portrayal in order to not repeat it and do his own portrayal on the character. Judging by trailers and the novel i read, it seems to me this Luthor is a lot darker than Hackman's, but still with amounts of quirky wit, such as here:
LUTHOR: go ahead, lemme hear you say it, just once
LOIS: you're insane
LUTHOR: no! *laughs* not that, no, the other thing *leans ear in*
LOIS: Superman will never--
LUTHOR: WRONG!!!!!!!!!!!!!!!!!
but at the same time as there being comicalness, there seems to be a great deal of darkness in the portrayal, because, and i hope i'm not giving too much away here, in the novel i read, Luthor actually finds a way to personally beat the living snot out of Superman, and even come VERY close to KILLING him!
hope that helped u understand
