In which episode of 'The Simpsons' did Stephen Hawking make his first appearance?

Stephen Hawking first appeared on The Simpsons in “They Saved Lisa’s Brain.”

The episode is the twenty-second and penultimate installment of season 10, first broadcast in the United States on May 9, 1999. Lisa joins Springfield’s Mensa chapter after writing a thoughtful letter to the Springfield Shopper, and the group briefly takes control of the town.

Hawking guest-starred as himself, using his distinctive computer-assisted voice. The episode’s central joke is that Springfield’s self-proclaimed intellectuals create an impractical utopia, prompting Hawking to evaluate their ideas—and Homer’s theory of a doughnut-shaped universe.

Viewers sometimes confuse this appearance with “The Springfield Files,” the season 8 episode featuring Leonard Nimoy and paranormal investigators, or with later Hawking cameos. He returned to The Simpsons several times, but “They Saved Lisa’s Brain” was his first appearance on the series.