Read and be enlightened.
History:
Doomsday was a creature born of genetic manipulation a long time ago. A scientist named Bertron had set up a laboratory on a distant and deadly world. There he and his team performed experiments on a living embryo. They ejected a living embryo into the harsh atmosphere, where it died instantly. The scientists then retrieved the embryo and regrew it in a regeneration pod, then repeated the process.
The experiment lasted for years. After several iterations, the creature developed the ability to survive in the planet's harsh atmosphere, only to be devoured by the vicious aliens which inhabited the world. Again and again Bertron and his team retrieved the remains of their project, which Bertron referred to as The Ultimate, and again and again The Ultimate was reborn and reinsterted into the atmosphere. And with each death and rebirth, The Ultimate retained the knowledge of its previous lives and learned from them.
Finally, after many many years of deaths and rebirths, The Ultimate became all that its creator envisioned. The Ultimate cleansed the entire planet of hostile life, and then came after Bertron. The Ultimate had retained all knowledge of its previous versions, including the knowledge and the face of the one person who continued to torment it.
The Ultimate fled from that hostile and harsh world by boarding one of the frequent supply ships which had enabled Bertron's experiment to continue for so long. From there he went on a world-by-world rampage, until he was finally killed on the peaceful planet Colu. The Coluans, unaware of The Ultimate's regenerative powers, buried it as they would one of their own--wrapped in green cloth and chained to a block of stone. The Coluans sent the stone into space, where it wandered for who knows how long a time before crash landing on Earth many years ago.
It began in a field several hundred miles outside of Metropolis, on a warm sunny afternoon. A low rumbling could be heard, growing louder and louder. Finally the source of this noise was revealed: a large, hulking behemoth, wrapped in green fabric and cables. This huge monster did not speak but instead began a murderous and seemingly random rampage.
The Justice League were the first to go up against this monster, who was quickly able to beat them all senseless. Superman arrived and found himself up against a being of such strength and mindless rage as he had never encountered before. This was Doomsday, and Superman's battle with him would prove to be his most difficult.
The monster Doomsday made his way towards the city of Metropolis, cutting a swath of destruction in his wake. Superman followed, and there, on the streets of the City of Tomorrow, right in front of the Daily Planet, the two fought a pitched battle. Onlookers were amazed and frightened to see the Man of Steel hurt, bruised, bleeding, and seemingly unable to subdue Doomsday. Windows shattered with the force of their blows, and the streets and buildings were torn to rubble. Then, finally, horribly, it happened. Although the Man of Steel was able to finally subdue and destroy the beast, the toll on his own body was too much. As the monster Doomsday fell to the ground, lifeless, so too did Superman.
The death of Superman was felt by all, but there was one individual who took it more personally even than the Man of Steel's closest friends. Lex Luthor had sworn that he would be the one who would kill Superman, and the monster Doomsday had beat him to the punch.
Doomsday's body was taken to Cadmus Laboratories for study, but one of the five Supermen who arrived in the wake of the true Superman's death arrived and removed the carcass into outer space. There the pretender Superman strapped the dead Doomsday to an asteroid and threw it deep into space. It floated there, lost among the stars, for a considerable time before a passing space freighter took note of the asteroid's mineral content. The freighter pulled the asteroid into her loading dock before realizing what was attached to it. The crew rushed to jettison the monster, but it was too late. Horribly, inexplicably, Doomsday came to life and slaughtered the ship's crew.
The ship, as it turns out, was en route to Apokolips, homeworld of the galactic despot Darkseid. The ship landed on autopilot and Doomsday emerged and began laying waste to the inhabitants of this new world. Even the great Darkseid himself proved vulnerable to the rampaging terror of Doomsday, his dread Omega Beams having no effect.
Meanwhile, back on Earth, the true Superman had returned from the dead. He learned of Doomsday's return and presence on Apokolips. Enlisting the aid of Waverider of the Linear Men, Superman travelled to Darkseid's homeworld to again do battle with Doomsday.
This unstoppable monster, who not only returned to life after each supposed killing but evolved past it, preventing the same method from proving lethal twice was the being Superman was travelling to face a second time.
On Apokolips, Superman and Waverider encountered Doomsday again, and also the traitorous Cyborg. Superman dealt with the Cyborg, with Darkseid's assistance. Waverider, curious to know the monster's true motivation, peered into Doomsday's mind and saw with horror that though the beast looked at Superman, the being it saw was Bertron! Waverider and Superman realized that the world Bertron had chosen to carry out his experiments was Krypton, and that it was Bertron's influence that sparked the Kryptonians' interest in genetic manipulation.
The battle on Apokolips was fierce. Even with the aid of a Mother Box, a living computer given him by Orion, Superman found himself unable to defeat Doomsday a second time. Finally, in desperation, Superman used one of Waverider's time/space travel devices to transport Doomsday to the End of Time, where the natural forces of entropy would quickly and finally defeat the monster.
Or so it was thought.
Doomsday surfaced yet a third time to menace the Man of Steel, and this time the rampaging monster was guided by an intelligence as sinister as it was vast. Superman learned to his horror that the monster Doomsday was inhabited by the consciousness of his foe Vril Dox, also known as Braniac.
This third encounter happened as Superman was trying to do a favor for his old friend and childhood sweetheart, Lana Lang, now married to Pete Ross. Lana's baby had been born prematurely, and needed to be taken to a major city hospital if he had any hope of survival. Lana persuaded Superman to make the trip, but along the way he was attacked by the newly intelligent Doomsday. Doomsday/Brainiac stole the young child, intending to use it as a new vessel to house Braniac's consciousness.
This time Superman knew what to do. Enlisting the aid of the JLA, Superman forced Doomsday/Brainiac into a teleportation tube, one of the many which the JLA used to travel back and forth from their headquarters on the moon. Then, before the monster could re-orient himself, Superman activated a perpetual loop between several of the transporter tubes. The tubes' frequencies were set to different levels, so that Doomsday would never fully materialize in any one of them long enough to escape or be freed.
This was the fate Superman designed for both Doomsday and Braniac: an eternity of perpetual motion, never resting in one transporter tube for very long, never completely there at any time. Unfortunately, Braniac was able to save his own consciousness at the last second, downloading himself into a new form, Braniac 2.5. 😎