4. Clint Eastwood
In 1993 episode 'Last Exit to Springfield', Lisa learns she needs braces, but Homer's boss at the Nuclear Power Plant, Mr Burns, has revoked the workers' dental plan, meaning Homer will have to pay for the braces himself. Homer is elected leader of the workers' union to campaign to get the dental plan reinstated and a series of accidental successes leads Mr Burns to consider Homer an integral member of the union and a master tactician, and eventually caves into the workers' demands. The role of Dr. Wolfe, the dentist in the episode, was offered to two Hollywood A-Listers - Anthony Hopkins and Clint Eastwood, but both declined the part and Anthony Perkins agreed to voice the character. Sadly, Perkins died of pneumonia before the role could be recorded and Simpsons regular Hank Azaria voiced Wolfe instead.