What is Doomsday and where did he come from?

The infamous Doomsday Vs. Superman battle in the Death of Superman saga from DC is among the most famous of all comic books. I personally own most of the saga and always counted among the legends. However, if there was a backstory to the villain I don't own it.

Where did Doomsday come from? What is he?

I'm looking for canon answers, from the ORIGINAL comics from the 90's. None of the new(er) animated movie stuff.