Doomsday

Born without a name, Doomsday was a biological weapon developed to explore the ultimate end potential of Celestial genetic code.

The Doomsday creature was engineered on a world formerly part of the Kryptonian Hegemony. During the years when the Kryptonians were being forced back to their homeworld, an alien scientist working at the behest of the Guardians of the Universe tried to design a beast that could be a physical match to Kryptonians.

The prototypes possessed genetic memory and evolutionary adaptation. Kryptonian prisoners were supercharged under synthetic sunlight and forced to fight the creature. Every time it was killed, it was brought back to life with a knowledge of how it died. Over time, forced evolution became natural, and the regeneration autonomous from the control of the scientists. It learned to absorb hyperspace energy the same way that Kryptonians naturally did and developed significant resistance to the fundamental energies of magic.

In short order the monster grew beyond all control and broke loose. It destroyed the labs and slaughtered every living sentient on the planet. Hundreds of Green Lanterns were dispatched to contain it; they all died as well. In desperation, seismic pulse-bombs were detonated near the core, rupturing the planet and destroying it utterly.

The creature somehow survived and was flung into deep space. Periodically it would be caught in a gravity well or picked up by a passing ship looking for salvage. At one point it took control of a spacecraft and made a line directly for Oa, slaughtering legions of Green Lanterns until the Guardians themselves joined the fray and ejected Doomsday at escape velocity once more. Doomsday would crash into a world once every few millennia and slaughter until he was defeated or there was no one left. The collective consciousness of an entire planet was gathered to defeat him on Calaton, and there Doomsday seemed to die before being punted into a fold in space-time.

Thrown into a dimensional void, Doomsday was eventually pulled into the stellar regions around the Demiurge. The casket containing his body crashed to ground on Earth and the monster emerged freshly invigorated. A hundred and fifty metahumans attempted to stop Doomsday over the course of the days-long rampage. A few were successful in temporarily halting him, but he would regenerate and return with fresh rage and a new tolerance for their means. Many civilian lives were lost and the Titans experienced two fatalities among their teammates. Finally, Superman joined the fray and went toe-to-toe with Doomsday. The end result was the defeated monster being hurled into The Phantom Zone, and many dead heroes to be mourned-- Superman among them.