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Happy Days (1978)
Williams got his big break in 1978 when he auditioned to play alien Mork from the planet Ork on Happy Days, making a lasting first impression on producer Garry Marshall by sitting on his head when he was asked to take a seat. Mork proved to be so popular that it led to a spin-off, Mork & Mindy. Williams returned for a guest appearance in Season 6.