Doctor Phoenix was actually an Abominable Snowman who was convinced he had to destroy the world because it was only a bad dream he was trapped in.
When the Kryptonian survivor Kal-El came to Earth as an infant, the presence of his alien aura on Earth somehow disrupted the Abominable Snowman's sleep-state and forced him to assume human form. Doctor Phoenix spent the next 27 years trying to discover a means through combined science and sorcery of returning to the world of dreams that he considered his personal reality and banishing the real world, whose noise and discordance caused Phoenix to regard it as a waking nightmare. Eventually, Superman succeeded in solving the problem and returning the Snowman to his permanent sleep state.
