Can you imagine the movie Beverly Hills Cop with no comedy? That was a distinct possibility before Eddie Murphy took over the role from Sylvester Stallone. Casting actors in a movie is crucial for its success, and it's hard to imagine an iconic film any other way after we've all seen the finished product. But in their early stages, many productions could have gone a very different way.
See 12 casting choices that changed in a pictofacts post at Cracked. And then imagine how those movies might have been different.