You were a Hyperion lab experiment. After you escaped, you went to live with a group of psychos and marauders, the flesh-rippers. You've been living with them for about four years, and have been hearing all about the vault Handsome Jack is trying to open, and the vault hunters (Krieg, Zer0, Axton, Roland, Brick, Mordecai, Hammerlock, Steve) were in Sanctuary trying to stop it.