The episode: Unproduced sequel to “Stark Raving Dad”
The role: “Prince”/Leon Kompowsky
What happened: Homer’s friend Leon Kompowsky was scheduled to return, this time under the delusion that he was Prince. Prince accepted the role, but there was some confusion over the script. The version he had received was apparently not the actual script — and he refused to do anything other than the script he’d been given.
The episode: “Marge vs. the Monorail”
The role: George Takei
What happened: Takei had already appeared in the episode “One Fish, Two Fish, Blowfish, Blue Fish,” but he did not want to appear in an episode that mocked public transporation because he was a member of the board of directors of the Southern California Rapid Transit District. His part was rewritten as fellow Star Trek actor Leonard Nimoy, voicing himself.
Clint Eastwood, Anthony Hopkins, and Anthony Perkins
The episode: “Last Exit to Springfield”
The role: Dr. Wolfe
What happened: Both Clint Eastwood and Anthony Hopkins turned down the role of the deranged dentist. Anthony Perkins actually agreed to do the part, but he died before he could record it. Hank Azaria ended up doing the voice.
The episode: “Last Tap Dance in Springfield”
The role: Vicki Valentine
What happened: Shirley Temple was allegedly offered the role of Vicki Valentine, an embittered former child star clearly modeled after Temple. Unamused, Temple told producers to “F off.” Allegedly.
Richard Nixon, Gerald Ford, Jimmy Carter, and Ronald Reagan
The episode: “Krusty Gets Kancelled”
The role: Richard Nixon, Gerald Ford, Jimmy Carter, and Ronald Reagan
What happened: It’s not surprising that the four living ex-presidents at the time of the episode did not want to appear on The Simpsons. In fact, Reagan is the only one of the four who responded at all, declining the offer.
READ THE FULL LIST OVER AT BUZZFEED
Mods, I lowered the list down to 5 items, but seriously, there are like 30 items at the source, and we have to stick to 5 regardless? It's like, why even bother? But I edited it anyway, so please post since I already went through the effort. Thank you. :)