Apparently banished from his world thousands of years ago, Unicron travels the galaxy, devouring planets to quench his hunger and taking their populations as slaves to maintain his inner body works. He runs into trouble when attacking Earth. A strange set of non-human creatures oppose Unicron, threatening to attack him with a metal-devouring organic spore. Before the two sides can annihilate each other, they reach an agreement favoring both parties. The creatures will go into hiding, allowing humanity to develop. When they reach a sufficient technological level to serve as slaves for Unicron's inner workings, they will call Unicron. He will destroy humanity and they will inherit the human-free world he leaves behind. Thousands of years later the pact is kept and the creatures, now calling themselves Cobra-La, summon Unicron via a beacon. After attacking a pirate vessel on the outskirts of a solar system, Unicron journeys to Earth. Hailed as the "Doom Star" by terrified humans, Unicron transforms to robot mode and prepares to destroy humanity. He is thwarted when Cosmos and Flint travel through his mouth into his body bearing the metal-eating spores of Cobra-La. Despite the best efforts of his "anti-bodies" (the Beastformers), they deliver the spores directly to his brain. He is last seen entering convulsions, indicating he is no longer a threat. It is later mentioned his body is floating around Earth.