As they often say in Hollywood, casting is 90% of directing. And when a film is cast well, it becomes nearly impossible to imagine the characters played by anyone other than the actors chosen.

The idea of someone other than Tom Hanks playing Forrest Gump seems preposterous. It feels like Matthew Broderick was born to play Ferris Bueller. These characters are iconic and filmgoers’ perceptions of them are inseparable from the actors who play them.

Yet these roles — along with many others — came surprisingly to being played by others. In each case, the part was offered to a different actor prior to being offered to the one who ultimately played it.

24/7 Tempo has identified 30 actors who turned down roles in movies that would go on to become box office blockbusters. These are the highest grossing films of all time.

Click here to see the actors who turned down blockbuster roles.

There are many reasons that an actor may turn down a part. Oftentimes, it comes down to scheduling. If an actor has signed on to star in one film, he or she may not be able to appear in a second one at the same time. Actors may also be under contract that prevents them from doing certain kinds of work. This was the case with Tom Selleck, who was under contract for the television show “Magnum P.I.” and was forced to turn down an offer to play Indiana Jones in “Raiders of the Lost Ark.” In some instances, actors simply fail to recognize the potential of a great script and as a result miss out on a great opportunity.

All of the actors included on our list have had successful careers — despite turning down these roles. These are the actors with the longest careers. The actors who passed on these opportunities, however, have likely lost out on millions of dollars, potential Academy Awards, and critical praise.