Megatron (Transformers Prime..)

The incredibly powerful Megatron is, in many ways, a fallen hero. He rose from the oppressed lower worker castes of Kaon to become a champion in the region's illegal deathmatches, casting aside his D-16 designation and taking the legendary name Megatronus[1] as his own. He called for an end to Cybertron's decrepit caste system and told the oppressed that the freedom of self-determination was the right of all sentient beings.

But absolute power corrupts absolutely, and Megatron's Decepticon revolution, like many similar movements, eventually spiraled into a new tyranny. Powerful, charismatic, violent, and filled with rage against anyone who stood in the way of his ambition and determination, Megatron drove Cybertron back from the brink of destruction. Now he and his former brother-in-arms Optimus Prime fight on other worlds. Megatron will never forgive Optimus for "betraying" him, robbing the Council of the rank of Prime that was rightfully his. He has reserved for his old friend the highest honor possible: a glorious death at his hands.

Megatron left three years ago, but now he's back. He's brought the monstrous Dark Energon to Earth and may very well have left his sanity in space. Though he's made some mistakes, he has no intention of making them again!