Unicron

Unicron is a Primordial God who became a gargantuan robotic organism and the ancient enemy of the Cybertronian God Primus.

Appearance
Unicron is a Cybertronian-like entity scaling at a planet-level size with orange, white, and grey armor. He has six horn-like protrusions stemming from his shoulders and two horns on his head.

Powers and abilities
Unicron possesses transformation abilities akin to Cybertronians, his alternate mode being a metallic planet akin to Cybertron.

Unicron can resurrect and reformat deceased Cybertronians into his heralds. For example, Primax iterations of Unicron have reformatted Decepticon leader Megatron into the far more powerful Galvatron. He has also reformatted Autobot leader Optimus Prime into the darker Nemesis Prime.

Unicron can create vast armies of drones such as Dead End Drones and undead Terrorcons, the latter of which is powered by Dark Energon, Unicron's lifeforce.

Unicron can give immense power to whoever he chooses as heralds.

History
Unicron is the enemy of all Transformer factions, being the fabled destroyer of Cybertron. His existence goes back probably to the very creation of the Cybertronians. However, it is debated as to whether he had disguised himself as a moon to transcend the countless ages or was trapped in that form by Primus. It is possible that he is the largest and most powerful Transfomer in existence (with the exception of Primus who is secretly the planet Cybertron itself and larger although not quite as powerful).

Unicron has been defeated many times but never totally destroyed; one of these was when both the Decepticons and the Autobots set aside their war and joined forces to defeat Unicron and stop him from destroying Cybertron.