Unicron is an ancient evil that serves no master.
History[]
Unicron's early history is unknown, as he simply appeared and began destroying planets one by one. When he approached the world of Cybertron, a united force of Autobots and Decepticons were there to meet him. The army defeated the goliath, destroying everything but his head. This remained in orbit around Cybertron as a grisly monument to Unicron's rampage.
Several years later, a Decepticon attempted to reactivate Unicron. He succeeded, and promised Unicron a body if he would help him controlled Cybertron. Unicron killed him, and merged his remains with the Decepticon, creating a behemoth that dwarfed most Transformers, but was tiny compared to his old body.