Caan vs Evans
James Caan played Sonny Corleone. Fans of the film loved his depiction of the character, but producer Robert Evans didn't. In fact, he cut over 45 minutes of footage with Caan in it, which totally limited his screen time and the depth of the character. Caan eventually confronted Evans about it, but no resolution happened.
The Two Dons
Robert De Niro played Don Vito in The Godfather II and Marlon Brando played Don Vito in The Godfather. Both actors won the Academy Award for Best Actor for their roles. This means that they are the only actors who won academy awards for playing the same character!