The Burner Doctor was a version of the Doctor who existed in an alternative timeline.
Biography
During his first incarnation, the Doctor had to leave Gallifrey after challenging the Time Lords' temporal intervention policy. He faced erasure from the timeline by his brother Braxiatel. Braxiatel was killed by the Doctor, who adopted that title, stole a TARDIS and fled Gallifrey to challenge the Time Lords' supposed right to rewrite history.
During his sixth incarnation, the Doctor was captured by the Time Lords and put on trial. The outcome resulted in his reintegration into Time Lord society. By the time that Lady President Romana came to power, the Doctor had adopted the title "Lord Burner" and the role of the President's personal temporal assassin who "burned" people from history, a role previously held by Braxiatel in both the proper and alternative timelines.
After meeting an alternative version of his brother, Lord Burner attempted to assassinate him on the Axis. During the fight, they fell into one of the Axis' portals with no set coordinates. Braxiatel found his way back to the proper timeline. (AUDIO: Disassembled)
As was the case with his counterpart in the main timeline, the Burner Doctor was put on trial by his own people during his sixth incarnation. (TV: The Trial of a Time Lord; AUDIO: Disassembled)