Red Hood

Jason Todd was the second Robin to work under Batman. He was killed by the Joker, yet was resurrected later by Ra's al Ghul via the Lazarus Pits. The newly resurrected Todd was pissed at Batman for not avenging his murder (and for replacing him with Tim Drake, the third Robin), so he took up the title of the Red Hood, and became a psychotic gun-toting vigilante. He's pretty much the black sheep of the Batfamily.