Doomsday

Long before Kryptonians inhabited their eponymous planet, it was home to a scientist of unknown species named Bertron that repeatedly experimented on an artificial being that was meant to be the most dangerous animal in the galaxy. The idea was that it was sent into battle to be killed, and then upon recreation, would become impervious to the way it was killed before. This alien, branded 'Doomsday', would break out of captivity, kill Bertron and lay waste to his lab as vengeance for experimenting on him in the first place, and then come to Earth at some point. Upon reawakening, it wreaked havoc across its entire journey across America, disposing of the Justice League before coming into contact with Superman. They engaged in a ferocious battle that trashed a good amount of Metropolis, eventually ending up in a draw that cost both their lives. Since then, after Superman’s revival, as expected, Doomsday would come back numerous other times, but was always brought down in a different way.

Bred to be the ultimate killing machine, Doomsday originated on Krypton, long before Superman's race was born. Besides giving him super powers, Doomsday’s DNA contains an innate hatred for all life.

Since killing him would be next to impossible, Superman devised a collar that allows him to control Doomsday’s movements. Doomsday now serves as a last resort weapon for the One Earth Regime.

The mainstream universe Doomsday first appears alongside the group of villains assembled by Lex Luthor to occupy the Justice League while the Joker prepares to detonate a nuke in the center of Metropolis. He appears and knocks away Superman as the other JLA members attack. Doomsday is later seen grabbing Hawkgirl's mace before being thrown to the ground by Green Lantern and Wonder Woman. He then attempts to attack Flash and Green Arrow before being taken into deep space by Superman. 

In the alternate timeline, Doomsday is used as a tool by the Regime, kept chained in the Fortress of Solitude. Regime Superman is shown to use a Kryptonian control collar to override Doomsday's actions. Upon discovering his friend Lex Luthor aided the Insurgency, Superman kills him and decides to show the world the true chaos that would arise without him by destroying Metropolis and Gotham City. Doomsday aids in the attack on Metropolis, toppling buildings one after the other with a single headbutt.

After the Regime's Black Adam and Aquaman are defeated by the mainstream Superman, Doomsday attacks Superman. To avoid causing collateral damage, Superman flies a berserk, reluctant Doomsday to the Fortress of Solitude. Doomsday then exclaims to Superman "I live to kill you", befor