Clifford C. "Cliff" Clavin, Jr. (born 1947 or 1949), is a fictional character on the American television show Cheers co-created (and 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 St.