Eric Stoltz: Back to the Future (as Marty McFly)
This was a decision made after getting a considerable amount of tape. As the story went, Stoltz was pegged as the original Marty McFly. Reports indicate he shot weeks worth of scenes for the movie before those in charge realized something was off. Stoltz apparently approached the role in a far more serious/introspective manner (clips can be seen on YouTube). As such, the move was made to bring on Michael J. Fox — a performer with more of a comedic feel.
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