Robin Williams became a television star after John Byner withdrew from playing the alien Mork in an episode of Happy Days, opening the role to Williams. The article presents the casting change as a pivotal moment: Williams’s performance led directly to the spin-off Mork & Mindy and accelerated his rise to mainstream fame.

Williams first appeared as Mork in the February 1978 Happy Days episode ‘My Favourite Orkan’, when the programme averaged more than 31 million viewers weekly. Mork & Mindy premiered seven months later, averaged nearly 29 million viewers in its first season and became America’s third most-watched television show; it ran for four series and earned Williams a Golden Globe.