Clifford C. Clavin, Jr.[2] (born 1947[3] or 1949) is a fictional character on the American television show Cheers played by John Ratzenberger.

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.

[5] Since Wendt was cast as George (who evolved into Norm Peterson),[6] Ratzenberger suggested to the producers that a know-it-all character should be added; this led to the creation of Cliff Clavin.

He lives with his mother, Esther Clavin (Frances Sternhagen)—first in his childhood two-story house (which was bulldozed in the sixth season's "The Last Angry Mailman" after Esther sold it to a convenience-store builder), and then in a condominium (which first appears in the season 6 episode "My Fair Clavin") with a sofabed.

He is ridiculed by friends and enemies alike, including Carla (Rhea Perlman) and Norm, for his know-it-all attitude.

", where he wins $22,000 in the first two rounds with questions that favor him, but loses it all with a wrong answer in Final Jeopardy (launching into a tirade which frightens host Alex Trebek).

He then has a relationship with fellow postal worker Margaret O'Keefe (Annie Golden) since Cheers' seventh season (1988–89).

In another Frasier episode, "Cheerful Goodbyes", Cliff has his retirement party at the airport bar; he had planned to move to Florida, but decides to stay in Boston (to Carla's dismay).

On the NBC News website, Wendall Wittler called Cliff a "classic" character; however, Wittler found his friendship with Norm Peterson "superficial" and unworthy of comparison with the relationship between Ralph Kramden (Jackie Gleason) and Ed Norton (Art Carney) on The Honeymooners.

In his book Hope, Andrew Razeghi described Cliff as a poster child for psychologist J. P. Guilford for a response to the Final Jeopardy!

The company operated airport lounges styled similarly to Cheers which included two robots, one heavyset and the other a postal worker, which the actors claimed resembled Cliff Clavin and Norm Peterson.

At the first, the judge ruled that the defendant did not violate copyright because Paramount Pictures had already granted it a license to produce Cheers-based bars.