The Death of Superman

Origins
Doomsday is a living weapon created created in a lab during the Kryptonian-Calatonian war. General Dru-Zod released this biological weapon of mass destruction and the entire Kryptonian War Fleet upon the Calatonian people, until there was no trace of them.

After the Kryptonians reined this monstrosity back in and placed it in cryogenic stasis, Zod was imprisoned in the Phantom Zone for his war crimes, and the Guild of War requested the aid of Zor-El and Alura in the creation of a military A.I. which would prevent another madman like Zod from ever hijacking the Kryptonian Fleet again. What they created was Brainiac and in a few years’ time, the Kryptonians went the way of the Calatoninas, destroyed in the exact same manner as Brainiac unleashed not just the War Fleet upon their home planet’s core, but also this savage weapon upon the population centers. When Krypton was in ruins, Brainiac put this creature back on ice and added it to its menagerie.

The Death of Superman
When Brainiac came to Earth, decades later, it came to kill Superman and Supergirl, but after losing several versions of its hardware to Superman and the Justice League, Brainiac plotted to download his mind into this xenocidal creation to create Brainiac 6.0. Brainiac hoped that the creature’s ability to adapt to survive would allow its mind to evolve to accept Brainiac’s consciousness, but Brainiac miscalculated and the creature evolved to reject Brainiac’s upload and escaped.

Unfortunately the creature came to Earth, still programmed to exterminate Kryptonians. This thing destroyed dozens of city blocks in three cities in its attempt to kill Superman. Over the course of the battle it turned out it was powerful enough to hurt Superman and beat him into a coma. He was evacuated by Blue Beetle and Booster Gold (first who managed to get there) and A.R.G.U.S. agent Alex Parker.

Because Doomsday was programmed to kill Kryptonians, the Justice League was able to use Power Girl as a bait to lure this “Doomsday” to the Fortress of Solitude where they imprisoned it in the Phantom Zone.

Aftermath
Doomsday has spent couple of years in the Phantom Zone plaing with the prisoners. When he failed to kill the Challengers, the Anti-Monitor has released him and sent him to planet Daxom.

Superman managed to survive, but it took him some time to recuperate when he was in a coma.

Trivia

 * Booster Gold gave Doomsday his name after he saw it beating Superman and say that that was Doomsday.