As originally presented in the Post-Crisis version of the DC Comics Universe, Lex Luthor is a product of child abuse and early poverty. Born in the Suicide Slum district of Metropolis, he is instilled with a desire to become a self-made man of great power and influence.

What planet is Lex Luthor from?

That planet would come to be called Lexor. Lexor was a world that orbited a red sun, where Lex Luthor earned the admiration of the people by restoring their lost technology. It was arid until Lex's intervention, and they made him their leader and revered him like a messiah; even naming the planet "Lexor" in his honor.

What ethnicity is Lex Luthor?

He also studied psychology and was a WWII soldier.) So mystery solved: Lex Luthor is Greek.