"Nobody calls me "Mad Dog"! Especially not some duded-up, egg-suckin' gutter trash!" ― Tannen after 'Clint Eastwood' (Marty McFly) accidentally gets on his bad side.
Buford "Mad Dog" Tannen is the posthumous overarching antagonist of the Back to the Future trilogy, serving as a cameo character in Back to the Future Part II and the main antagonist of Back to the Future Part III.
An outlaw living in the latter half of the 19th century, he lived around Hill Valley, California. Tannen was the great-grandfather of Biff Tannen.
He is portrayed by Thomas F. Wilson, who also played Biff and Griff Tannen.