The Joker is an iconic comic book character and it's not surprising that some actors with a geeky side long to play the villian. Most notably, Robin Williams almost got to play The Joker in the 1989 film, but Jack Nicoloson was originally offered the part and when they approached Williams with the role, Nicoloson changed his mind. Williams was also almost cast as The Riddler in the 1995 film, but Jim Carrey was picked over him. While it's sad that comic-book fan Robin Williams never got to act in one of the Batman films, it's probably best for his legacy that he wasn't cast in that trainwreck.
Learn about 9 other actors who almost played The Joker here.