Alexander Luthor Junior was the son of Earth-Three's only super-hero, Alexander Luthor Senior. He was the sole survivor of Earth-Three after it was destroyed in the Crisis on Infinite Earths. Along with Superman and Lois Lane of Earth-Two, and Superboy of Earth-Prime, Alex entered a paradise-like dimension where the four could live eternally following the Crisis and the creation of New Earth. However, Luthor and Superboy-Prime became restless, and eventually Luthor worked out a plan to escape and recreate their own Earths. Reaching New Earth, Luthor fooled the Society (aka the Secret Society of Super-Villains) into helping him. However, his plans all failed and he was later killed by the Joker of Earth-One.
During the Blackest Night event, Luthor was revived as a Black Lantern, but finally destroyed again.