It nearly happened but Sean Connery turned down The Lord of the Rings because he “didn’t understand it”. Too bad, I actually think he would have done quite well in the role.
Sometimes I wonder what the casting directors are thining in movies like Will Smith almost got to play Neo in The Matrix. There are some very interesting almost film moments and you can see them all at notstarring.com Some of my favorites are Jim Carrey as Howard Huges instead of Leonardo DiCaprio in The Aviator, John Travolta as Melvin in As Good As it Gets and Gus Van Saint wanted to directed Broke Back Mountain, that would have been a totally different movie.
Looking at that website reminded me that what makes a story good has a lot to do with the people who end up telling it.