Cybertronian ID: Master Chief (Sierra-117)

At the end of Halo: 3, the Master Chief managed to save the Universe from total annihilation by eliminating the Ark. Unfortunately, the success of this mission came with the price of the Spartan-II's life, leaving humanity to mourn the loss of their greatest hero.

However, this was not the end of the Master Chief's story; Through unspecified means, he was reborn as a large Cybertronian warrior and located by Ultra Magnus. The blue Mech offered the Master Chief a chance to fight for the Autobot cause, and defend the universe from the merciless claws of the Decepticons.

Nothing ever seems to go right for the Spartan-II.