Alexander Luther, Jr. is the son of Lex Luthor and Lois Lane from a different universe in which Lex is Earth's
greatest hero and Superman is a terrible villain.
During the Crisis on Infinite Earths, his Earth was erased from existance. He was rescued from his dimension by the Monitor, as he was destined to play a huge role in the crisis to come. He was one of four characters to survive the restructuring of the universe, stuck eternally in a paradise dimension.
He and Superboy-Prime escaped the paradise dimension in Infinite Crisis. Outside, they formulated a plot to restore their respective worlds. To this end, Alex disguised himself as the Lex Luthor of the current Earth, and organized many supervillains into a new society. His plan failed, and after the crisis ended, he was killed by the true Luthor and the Joker.