Cliff Clavin
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 resident know-it-all. 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.