Tiny Tina is a new NPC in Borderlands 2. She is described in-game as "The world's deadliest 13-year-old." She has a warped perception of reality, likely resulting from the psychological trauma she suffered at the hands of Flesh-Stick's bandits who, among other things, killed both her parents. As a result, she is trying to hunt down Flesh-Stick and, in the process, take out as many Bandits as possible.
Tiny Tina is voiced by Ash Burch, of "Hey Ash, Whatcha Playin'?" internet fame.