According to Wikipedia,
John Dezso Ratzenberger is an American actor, comedian and director. He is best known for playing the character Cliff Clavin on the comedy series Cheers, for which he earned two Primetime Emmy nominations. He also played a role in the short-lived spin-off The Tortellis and in an episode of Wings, which was made by the same creators. Ratzenberger voiced various characters in Pixar Animation Studios' feature films, including Hamm in the Toy Story franchise, The Abominable Snowman in the Monsters, Inc. franchise, Mack in the Cars franchise, The Underminer in The Incredibles franchise, and many others.
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