Unicron

Unicron was a fallen god from before the universe existed, who sought the ultimate peace that would be granted by the destruction of all life. Amazingly, Unicron accomplished this task, wiping out all life, planets, stars and nebulae, even "the stuff of space itself" in the universe and leaving only nothingness and void. His lust for destruction finally sated, Unicron entered a deep sleep - but he had not been thorough enough. Tiny fragments of the old universe reacted with each other, and a new universe was born. As Unicron slept, the core of this new universe - somehow a sentient being - became aware of Unicron's threat and created a defender to battle his evil - Primus, the lord of light.

Unicron awoke to find himself surrounded by another universe, and simply began to destroy it again.