Unicron

 

The most powerful Transformer ever created was the mighty Unicron.  Built by the nigh eve Primacron, Unicron was to be his ultimate weapon.  However, Unicron did not like this idea and soon turned on Primacron, leaving him a broken a battered being.  Unicron then went off in the galaxy devouring planets that he came across to feed his insatiable appetite.

Eventually, Unicron learned of one item that could destroy him, the Autobot Matrix of Leadership, which had the combined knowledge of all Autobot Leaders in it.  In his quest to destroy the Matrix, Unicron made a deal with the badly damaged Megatron.  In exchange for a new body, Megatron would destroy the Matrix, which at that time had been passed on to Ultra Magnus by Optimus Prime.  Agreeing to this deal, Unicron changed Megatron into the mighty Galvatron, and then several of his warriors into Cyclonus, Scourge, and the Sweeps.

Though Galvatron did succeed in taking the Matrix from Ultra Magnus, he decided to betray Unicron, and use it on his former master.  This plan proved to be fool hearty, since only the true leader of the Autobot's could open the Matrix.  Unicron's HeadFor his actions, Galvatron turned Unicron's wrath onto Cybertron itself.  It was of course during this battle that the Autobot Hotshot found the Matrix, thus changing himself into Rodimus Prime, and used it to destroy Unicron's body, and sending his head into orbit of Cybertron.

Many hoped that this would be the end of their troubles with Unicron, but it was soon found out that though his body was destroyed by the power of the Matrix of Leadership, Unicron still lived in a form of Stasis Lock.  It was not until Starscream returned from the dead, that the Autobot's began to worry about Unicron again.  Starscream reactivated Unicron and asked for a new body.  Unicron agreed to do so, only if Starscream completed 3 tasks for him.  The 1st was to steel the Eyes of Metroplex.  The 2nd was to bring Tripticon to him, and then place the giants Transformation Cog in Unicron.  The last, was to hook Unicron's head up to Cybertron.

Fortunately by this time, the Autobot's had been warned about Unicron's plan and had set up a powerful explosive charge that sent Unicron's head, as well as Starscream out into space.  In order to prevent this from ever happening again, the Autobot's took Unicron's head out of Cybertron's orbit, and sent it on a direct course into a nearby star, thus ending the terror of Unicron once and for all.