9. Alex Murphy - Robocop 3
Peter Weller made a name for himself as the titular hero in both Robocop and Robocop 2, but when it came time to make a third film in the franchise, Weller wasn't involved. That left the filmmakers with a bit of a problem since Weller had done a great job creating the character.
To get things going for the second sequel, a new actor was brought on board to play Alex Murphy/Robocop. Weller would have reprised his role, but he was busy filming Naked Lunch at the time. Robert John Burke put on the costume and fought a cybernetic ninja (really) in the third installment in the franchise, but several issues made his job all the more difficult.
While it's not easy to fill anyone's shoes in a role they performed in two movies, it was literally difficult for Burke. He was given the suit made for Robocop 2, which was form-fitted for Weller's use. As Burke was several inches taller than Weller, just wearing the Robocop costume proved incredibly painful for the actor.
Burke's performance wasn't bad, but the movie itself was pretty awful. The "R" rating was dropped to cater to a younger audience, and that didn't help it in any way. Robocop 3 flopped with critics and audiences everywhere.