In the final panels of “Watchmen,” Doctor Manhattan tells Ozymandias he’s leaving their universe for a “simpler” one. When the story picks up again in “Doomsday Clock,” it’s revealed that Manhattan has left for the same universe that Superman and Batman exist in. In his omniscient state, the one thing he can’t see past is his initial encounter with Superman, which makes him wonder: “Does this mean he destroys me, or I destroy everything?”
Fascinated with this other being’s importance, Manhattan tinkers with the multiverse, altering timelines and events to see how various outcomes alter Superman’s perceptions, motives, and world views. In doing so, he learns this Man of Tomorrow represents a beacon of hope, whose very existence acts as an anchor to all the other worlds within the DC multiverse — making Superman’s world a sort of metaverse.
After coming to terms with this understanding, Superman helps Doctor Manhattan see it doesn’t have to be all hopeless destruction, and Manhattan uses his transcendence of time and space to eliminate nuclear bombs — and go back in time to prevent his transformative accident from happening. In the process, DC is able to tie up loose ends from conflicting multiverses, and launch a clean slate for fresh canon under the 2016 “Rebirth” launch. All’s well that ends well — but how many lives were destroyed along the way?