Borderlands 2's Krieg is a psycho, but he's also one of the good guys. A new trailer shows how he meets up with the Siren, Maya, and attempts to save her life after he comes under fire from her on his way to Pandora. The video itself is set prior to the events of the game.
He's schizophrenic, and his intelligence is unable to manifest itself as the only words that come out of his mouth are incoherent yelling about poop trains and riding meat bicycles.
This one time, he manages to communicate his true thoughts to Maya, and as a result, saves her life. She repays him in kind by saving his life just seconds thereafter, and the two Vault Hunters make their way to the game's beginning.
Krieg is currently available as a downloadable DLC character for the PC, Xbox 360 and PlayStation 3.