Doomsday is a mutated clone of the Kryptonian Superman. He was created by Project Cadmus as a contingency in case Superman ever went rogue again. However, he was impossible to control and so Amanda Waller arranged for him to be blasted off into deep space. He eventually escaped and clashed with the Justice Lords Superman but ended up lobotomized. Later on, he would recover and clash with the Superman of his own universe. When it became apparent that he was a mindless killer who would not change his ways, Superman banished him to the Phantom Zone.