Four pages from ACTION COMICS 903...
Doomsday clones have been unleashed upon to Earth, each intent on bringing about doomsday in its own way. One's targeting a nuclear silo in Russia, another a fault line in Hawaii... and a third has set its eyes on a virus lab.
Meanwhile, at S.T.A.R. Labs, Superman and some scientists are analyzing an unconscious Doomsday, looking for clues, when it starts to wake up.
Superman goes after the culprit behind it all, the Doomslayer. The character has a kind of interesting backstory, or at least seems to based on what we can piece together from the hints. He's a Doomsday from millions of years in the future, possessed of intelligence but also a deep, overwhelming self-hatred at being a murderous engine of destruction. He's decided to go back in time and remove from the universe the blight that is himself, totally and thoroughly. And since Earth has the knowledge of how to clone Doomsday, that means one of his objectives is to destroy the planet, before that knowledge can spread to the stars.