Back To The Future might have had a completely different "feel" if they had stuck with the actor who was originally cast in the role - Eric Stoltz!
It's been said that C. Thomas Howell was also considered for the role, and Corey Hart was given the opportunity to screen test for the part. He turned it down to focus on his music.
I think we can all agree, nobody could have played that role quite like Michael J. Fox!