Unicron

Unicron, additionally titled the Chaos Bringer, Planet Eater, and Death God, is a central antagonist in the Transformers franchise, appearing in several pieces of the series' fiction. He is the twin brother of Primus, a benevolent force that created the Transformer race.

Creation
When the One, the actual heart of the universe, was years into its formation, it gave birth to Unicron. However, being the malevolent that he is, Unicron began devouring reality itself planet by planet so he can live in complete nothingness (or as he puts it, peace) once he's done ingesting the universe. As such, the One split Unicron in half, the other half forming an all-knowing robot god named Primus to stop his evil twin brother. The two siblings had a vicious battle, both of them learning how to transform into planets, and Primus spawned thirteen robotic warriors (much smaller than him) to assist him in his battle against the chaos bringer. However, one warrior betrayed Primus and sided with Unicron, yet despite this, Primus still won and banished the two warmongers from reality. This warrior was later labeled The Fallen. Even though Unicron was down, he wasn't out and continued to slowly float his way back to the reality before eating the universe, planet by planet.