It's hard to imagine anyone else playing the bright-eyed, guitar-playing, time-traveling teenager in Back to the Future (1985), but before Michael J. Fox signed on, Eric Stoltz was cast as Marty McFly. While Michael was director Robert Zemeckis' first choice, Michael's schedule on his hit TV series Family Ties wouldn't allow it, so Eric was brought in. But Robert soon realized the actor was a bit too intense for the role and was let go. As fate would have it, Michael's schedule opened up and he took over. Now that's heavy!