Doomsday was a "Kryptonian Deformity." He was created when Lex Luthor used the Genesis Chamber to splice his DNA with that of the deceased Zod's. His power is so mighty, that it not only challenges the combined strength of Batman, Superman and Wonder Woman, but also surpasses them. This massive power combined with his raging bloodlust and lack of rational thinking, makes him a being of Apocalyptic proportions.