Eric Stoltz(I)

He was cast as Marty McFly in Retour vers le futur (1985) after Robert Zemeckis and Bob Gale were unable to get Michael J. Fox, their first choice for the role, due to scheduling conflicts. After only five weeks of filming, he was let go from the film because Zemeckis and Gale thought he was "too intense" for the character. Fox, who by then was available, took over the role. Stoltz later went on to play the title role in La mouche II (1989) where his character's name was also Martin. So Stoltz went from playing Marty (short for Martin) McFly to Martin THE fly.

It's hard not to get a big head in the film industry, there are people on a set paid to cater to your every need, from the minute you arrive until you go home. It's kind of strange, but not unpleasant.