The being that would one day be known as "Doomsday" was born on the planet Krypton in prehistoric times, long before the humanoid Kryptonians rose to dominance 250,000 years before the planet's destruction. In this period, Krypton's environment was harsh and violent, suitable for only the absolute strongest of creatures to survive in. Bertron, an alien scientist who sought to create the perfect life-form, had bred an infant humanoid creature in his laboratory. This infant was then left to die in the harsh environment outside the lab and soon perished, but Bertron collected the infant's remains and used them to create a clone. The clone was stronger than the original, but still suffered a horrific death outside the lab, and from its remains a stronger clone was created. This process would continue for years, each clone being killed and remade stronger than the previous as a twisted form of artificial breeding. With each death, however, the creature's biological memory expanded and its body would adapt to withstand whatever had killed it previously. The agony of each death was recorded within the creature's very cells, driving it to hate all forms of life. It eventually became strong enough to easily withstand Krypton's inhospitable climate and it hunted down and slaughtered all of the predators that had killed its predecessors. The creature didn't stop until it had killed every native creature on the planet and eventually came for Bertron himself. Bertron's "Ultimate" had come home to avenge itself against its creator and tore the scientist apart.
Destroyer of Worlds
The Ultimate was able to escape Krypton by hitching a ride on a cargo shuttle that had previously made supply runs to Bertron's lab. Afterwards, it went on a killing spree across the universe, beginning with the planet Bylan 5 where the New God Darkseid was about to wed a princess (though only to obtain chemical deposits for Apokalips' weapon factories). The monster's rampage caused enough damage to render Bylan 5's atmosphere toxic, forcing the surviving inhabitants to flee. The Ultimate boarded one of the evacuating ships, killing all of its occupants and causing the vessel to crash-land on Khundia. The native clans of Khundia, formerly at war with one another, united out of desperation and built protective armor for a warrior named Kobald, who was hoped to survive long enough to force the Ultimate onto a rocket. Once the rocket was in space, the Ultimate killed Kobald and the resulting explosion sent him hurling through space.
As the Ultimate drifted through space, it encountered Zharan Pel of the Green Lantern Corps. After killing Pel and taking his Power Ring, the monster headed for the planet Oa, drawn by the power of the Guardians of the Universe. Almost the entire Green Lantern Corps was mobilized to stop the beast but many were slaughtered, until one of the Guardians sacrificed himself to the Ultimate. The release of energies by the Guardian caused a tear in space through which the Ultimate fell. Eventually coming to the planet Calaton, he ravaged that world for three years. With only the capital city left, the royal family combined their life forces into a single energy being, the Radiant. The Radiant killed the Ultimate with a huge blast of energy (laying waste to over a fifth of his planet in the process). In common Calatonian burial procedures, the Ultimate's seemingly-dead body was suited and shackled to prevent his spirit escaping into the afterlife, and he was shot into space due to his murders making him unworthy of burial on Calaton. Eventually, his metallic casket crashed on Earth, the force of the impact driving it deep underground.
The Death of Superman
In the 20th century AD, the Ultimate awoke within its casket and ripped its way out, burrowing up to the surface and finding itself in the midst of Midwestern America. In a world full of life, the creature had but one purpose: kill everything. It went on a rampage and murdered many innocent people, attracting the attention of the Justice League. The various League members tried to stop the monster but were beaten back, the creature's strength too much for any of them to handle. It was the hero Booster Gold who coined the name "Doomsday" as he remarked the fight to the media as "the coming of Doomsday". Since then, the creature has always been referred to as "Doomsday" by the people of Earth.
As Doomsday continued to carve a path of destruction across the Midwest, its attention was drawn to several billboards advertising violent wrestling competitions in Metropolis, which appealed to its murderous nature. It headed for the city and Superman knew that he could not allow the monster to reach Metropolis as fighting there could very well lead to the city being completely destroyed. As Superman attempted to stop Doomsday, the creature became aware of the Man of Steel's immense power, recognising him as a true threat and became intent on killing him specifically. Superman and Doomsday seemed to be equally matched in power, but Doomsday was unhindered by fear or compassion and cared nothing for the city and people around it, and so it held nothing back. If Superman was to defeat the creature, he would have to fight without restraint. The battle between the two titans concluded in front of the Daily Planet building, with both combatants apparently dying. The world mourned for Superman over the days that followed and Doomsday's body was later strapped to an asteroid and hurled into space, supposedly on a course that would never intersect with another planet.
Doomsday would return to life, however, eventually returning to Earth some time after Superman's resurrection and would terrorise the Man of Steel and his allies many times in the future.
Throughout most of its appearances, Doomsday has been depicted as a savage, mindless monster driven only to kill any and all life-forms it encounters. There have been occasions where Doomsday has developed a level of sentience and could even talk, though even this has done little to curb the creature's murderous instincts. However, with sentience has come a greater understanding of the concepts of emotion and Doomsday, normally unable to feel or even understand pain, was for a time capable of acknowledging it and even developed an inkling of fear, thereby diminishing its strength as it could not fight without restrictions as it did before. These states of sentience have never been permanent and Doomsday remains a ferocious, unstoppable engine of destruction.
- Superior Strength - Doomsday is physically the strongest humanoid being in the universe, capable of lifting many times its own weight. It can easily match Superman's strength.
- Regeneration - It is unknown what exactly Doomsday is made of, but it does not require food or rest and doesn't even need to breathe. It has no organs or even blood, its body is composed of completely solid matter. If Doomsday is wounded, the injury will instantly heal itself.
- Endurance and Adaptability - Doomsday is pretty much invincible as far as ordinary Earth-based weapons and tactics are involved. It is completely bulletproof and can withstand any temperatures and any environmental hazard. Every time Doomsday has been "killed", it has come back to life stronger than before with an added resistance to whatever had previously killed it, meaning that it can never die the same way twice.
- Immortality - Doomsday has lived for countless millenia, unaffected by age or environment. It has always come back to life after each "death", including occasions where its entire body has supposedly been destroyed at the molecular level.
Doomsday has no weaknesses whatsoever. Anything that has killed it before, it has since become immune to. There is no earthly weapon that can stop it and only the most skilled and powerful individuals - such as members of the Justice League - are capable of slowing it down or incapacitating it, and even then only temporarily.