The Burner Doctor was a version of the Doctor from an alternate universe.
Biography
The Burner Doctor had to leave Gallifrey after challenging the Time Lord Non-interference policy, where he faced erasure from the timeline by his brother Braxiatel. Braxiatel was killed by the Doctor, who then adopted that title, stole a TARDIS and fled Gallifrey to challenge the Time Lords' right to rewrite history.
During his sixth incarnation, the Doctor was captured by the Time Lords and put on trial, the outcome of which resulted in his reintegration into Time Lord society. By the time President Romana came to power, the Doctor had adopted the title "Lord Burner" and the role of the the President's personal temporal assassin who "burned" people from history; a role previously held by Braxiatel.
After meeting an alternate version of his brother, Irving Braxiatel, the Burner Doctor attempted to assassinate him on the Axis. During the fight they fell into one of the Axis's portals with no set co-ordinates; drifting through the timelines until they found their way into one. Whilst Braxiatel eventually found himself back in the Prime Timeline the fate of the Burner Doctor was unknown. (BFG: Disassembled)