Apollo 13 – John Travolta instead of Tom Hanks?
While the real Jim Lovell apparently thought that Kevin Costner would, by appearance, look more like him, Costner never tried out for the part. In fact, director Ron Howard went straight to Tom Hanks, knowing his interest in the matter, and Hanks agreed to join the cast.
Basic Instinct – Michelle Pfeifer, Kim Basinger, Meg Ryan, or Julia Roberts instead of Sharon Stone?
The role of Catherine was offered to a number of actresses who refused. Michelle Pfeiffer apparently found the nudity to be an obstacle. Sharon Stone in the end was the right choice. The role of the femme fatale Catherine meant for Sharon Stone a Golden Globe award for best actress, in addition to the famous, provocative leg-crossing scene, of course.
Gladiator – Mel Gibson instead of Russell Crowe?
Antonio Banderas and Mel Gibson were both considered for the role of Maximus, and both turned the offer down. In the end, the role went to Russell Crowe, who lost a significant weight for the film, and during shooting suffered several injuries. In spite of that, Maximus became his favourite character.
Jerry Maguire – could have been Tom Hanks instead of Tom Cruise
The character of Jerry Maguire in the screenplay was originally planned for Tom Hanks, who was unable to accept the role in the movie due to other commitments.
Raiders of the Lost Ark - Tom Selleck instead of Harrison Ford
The role of Indiana Jones was offered to Tom Selleck, who refused – same as Nick Nolte, Steve Martin, Chevy Chase, and Jack Nicholson. Harrison Ford was chosen only three weeks before shooting began.