Back to the Future's ending sees Marty replace another version of himself with a better life, but what happens to this version of the series hero?

Back to the Future Part III’s villain is the great-grandfather of Biff from Back to the Future, making him the great-great-great-grandfather of Biff's son Grizz from Back to the Future Part II.

However, Marty McFly - voiced by David Kaufman in the animated series - openly ponders whether every period they visit has its own past or future version of Biff Tannen. Either way, there's very ...