Before Krypton exploded and Jor-El put his baby son, Kal-El, in a rocket ship to Earth, the benevolent ruler was forced to banish three irredeemable criminals to another dimension called The Phantom Zone. The trio's leader, General Zod, vowed revenge. Later, of course, Kal-El grew up to become Superman, Earth's mighty champion. A battle with the criminal mastermind, Lex Luthor, ends with Superman hurling a nuclear warhead into space where it explodes, but not harmlessly. Instead, it frees the Kryptonian threesome from their other-dimensional prison. They soon discover they have almost unlimited power (the same powers, in fact, as Superman), which they use to take over the Earth.