Clifford C. Clavin, Jr. is a fictional character on the American television show Cheers played by John Ratzenberger. A postal worker, he is the bar's know-it-all and was a contestant on the game show Jeopardy! Cliff was not originally scripted in the series' pilot episode, "Give Me a Ring Sometime", but the producers decided to add a know-it-all character and Ratzenberger helped flesh it out. The actor made guest appearances as Cliff on The Tortellis, St. Elsewhere, Wings, and Frasier.

Cheers is an American sitcom television series that aired on NBC from September 30, 1982, to May 20, 1993, with a total of 275 episodes across eleven seasons. The show was produced by Charles/Burrows/Charles Productions in association with Paramount Network Television and was created by the team of James Burrows and Glen and Les Charles. The show is set in the titular bar in Boston, where a group of locals meet to drink, relax, socialize, and escape from their day to day issues.