"What Is... Cliff Clavin?" is the fourteenth episode of the eighth season of the American television sitcom Cheers, co-written by Dan O'Shannon and Tom Anderson, and directed by Andy Ackerman rather than James Burrows, who directed most of the other episodes of the series. It originally aired on January 18, 1990, on NBC.[2] In this episode, Cliff Clavin (John Ratzenberger) appears on the game show Jeopardy! and game show host Alex Trebek guest stars as himself. Cliff racks up an insurmountable lead during the game, only to lose it all in the final round. The episode received praise from critics for its concept and its guest star.