Casting is one of the most important and mysterious parts of filmmaking. Not only are actors selected based on their chemistry, skill, and buzz, there is also a whole mess of behind-the-scenes coordination. Actors have missed out on major career-defining roles for all sorts of reasons. Iconic roles like Indiana Jones, Wolverine, and Marty McFly all had different original actors. Careers, film history, and even a major celebrity marriage have all been forever altered by casting changes. Some actors have missed out on A-list careers. Here are a few of the most shocking movie casting changes.