Buford "Mad Dog" Tannen was an outlaw and ancestor of Biff Tannen who was the terror of Hill Valley in 1885. He hated his nickname, "Mad Dog." Buford was eventually defeated and humiliated by a time-displaced Emmett Brown and Marty McFly.
In the timeline before Marty interfered, Buford shot and killed Brown; this was averted by Marty's presence.
- Back to the Future Part III (1990)