6. George Takei
Though George Takei has appeared in The Simpsons no fewer than three times, in episodes such as 'One Fish, Two Fish, Blowfish, Blue Fish', 'The Old Man and the Key' and 'Thirty Minutes Over Tokyo', playing a different character each time, the Japanese actor declined to guest star in 'Marge vs. the Monorail'. Takei, best known for his role as Sulu in Star Trek and recently for being one of social media's most active celebrity users, apparently refused the 1993 role as he did not want to mock public transport, with the episode's plot focusing on Springfield's purchase of a monorail from a conman. In 'Marge vs. the Monorail', Marge attempts to expose corrupt Lyle Lanley who sells Springfield a faulty Monorail which runs on solar power, but malfunctions and picks up speed, unable to stop and putting the entire town in danger. Takei asked for script changes but failed, and instead, the role
went to fellow Star Trek actor Leonard Nimoy.