Marty McFly: Unlike many actors on this list, Michael J. Fox was the initial choice for the role that made him famous. Conflicts with his “Family Ties” shooting schedule nearly kept Fox out of “Back to the Future” and, for a time, he was replaced by Eric Stoltz. Fox returned to the role when Stoltz showed he wasn’t right for the part of a time traveling hero with his uber-serious approach. Producers worked with Fox’s TV schedule and the rest is history.