Biff Tannen is more of a fun bad guy -- we laugh at his stupidity and his lunk-headed attempts to make Marty McFly's life a living hell in the 'Back to the Future' trilogy (and it turns out the Tannen/McFly feud goes way, way back and way, way forward). But make no mistake: Biff is one serious bad guy. He might be a little dumb, but a dumb bad guy is almost as dangerous as a really smart one.