Action Comics
Adventures of Superman
Superman Vol. 2
Superman: The Doomsday Wars
Superman: The Man of Steel
Choosing the harshest environment on Krypton, with the most lethal native creatures known to exist in the universe, the scientists established a laboratory complex beneath a protective doom and began his experiments.
Starting his experiments with an infant not native to Krypton, he exiled the infant outside the protective dome, where it was quickly made a meal of by the creatures outside. Gathering a tissue sample from the remains the scientists cloned another infant.
Over the decades a clone would be grown from whatever remained, and exiled from the protective dome. Three decades later the infant was able to survive the environment and evade the native creatures for hours before being killed. After more years of evolution the clones were referred to as the Ultimate.
Exiled for two years, the Ultimate hunted the native creatures to their extinction. Eventually the Ultimate returned to the dome, smashing its way in and killing the scientists who had tortured it over the decades.
Wandering the planet in a murderous rage, fate intervened when the Ultimate smuggled aboard a supply ship unnoticed. Drifting throughout the galaxy the Ultimate became known as the engine of destruction, Doomsday.