According to the DVD special features, Crispin Glover auditioned for the role of Marty McFly before being cast as George (Marty's father).
Actor who got the part: Micheal J. Fox
The producers loved Crispin and offered him the part of Philo. Crispin read the script and said the only role he'd be interested in playing was "Crazy Ernie." They couldn't see him in the role.
Did you know that Crispin Glover was not the only choice for this movie? (click to learn more)