What is the origin of Doomsday?

I heard it was ancient Kryptonian scientists who created Doomsday and not a character named Bertron, but other than that, davoomac is right on the money. (Of course that's the kind of detail that gets retconned all the time. It's possible that when I researched the character a few years ago, it WAS Kryptonian scientists, and the writers changed that later. Or maybe I was just wrong.)

The irony is that Doomsday is a relic of Superman's alien heritage that returns to threaten him, sort of like Kryptonite. Having Kryptonian scientists create him works even better in this respect, since then Superman is sort of responsible for stopping Doomsday because of the sins of his ancestors. Man, it seems like everything that's left of Krypton except Superman is really bad for the rest of us--Doomsday, Zod, the Phantom Zone, one version of Brainiac, Kryptonite....it's hard to conceive of the planet as ever being a nice place to live, ya know?

Doomsday was artificially created in the distant past on Krypton, long before the humanoid Kryptonian race had gained dominance over the planet; in this time period, Krypton was a violent, hellish world where only the absolute strongest of creatures could survive (at the time, the world's dominant lifeforms were said to be the most dangerous creatures in the universe). Doomsday's creator was a mysterious alien named Bertron, who wished to create the ultimate lifeform. To do so, Bertron and his team sent a baby onto the surface of the planet, where it would be instantly killed by the harsh environment or the vicious creatures inhabiting it. Each time, whatever of the lifeform's remains that survived were harvested and used again, to create a better, stronger version than the previous. In short, the mad scientist was using the method of cloning to accelerate the evolution of the being he was creating. Through decades of this process, the being who would eventually become Doomsday was forced to endure the agony of death, thousands upon thousands of times; the memory of these countless deaths was recorded in his genes and drove it to hate all life. Eventually, Doomsday gained the ability to evolve against what killed him in his prior life without the need of Bertron's technology. At this point he proceeded to hunt down and kill all of the lethal creatures that inhabited Krypton. Bertron himself met his death at the hands of his own creation. Doomsday escaped Krypton and went on a killing spree across several planets, eventually coming to Calaton, where he was defeated by the energy being, The Radiant. In common Calatonian burial procedures, Doomsday's body was shackled and masked, and due to his status as a murderer, was shot into space. Eventually, he would land on Earth, the force of the impact of his landing driving the casket deep underground. Doomsday, however, was not dead, as any time he would be "killed", he would return evolved past whatever defeated him. ~wikipedia