A debunker is a person who attempts to expose or discredit claims believed to be false, exaggerated or pretentious. The term is closely associated with skeptical investigation of controversial topics such as U.F.O.s, claimed paranormal phenomena, cryptids, conspiracy theories, alternative medicine, religion, or exploratory or fringe areas of scientific or pseudoscientific research.

According to the Merriam-Webster online dictionary, "debunk" is defined as 1. Expose the falseness or hollowness of (a myth, idea, or belief). 2. Reduce the inflated reputation of (someone), esp. by ridicule: "comedy takes delight in debunking heroes". If debunkers are not careful, their communications may backfire – increasing an audience's long term belief in myths. Backfire effects can occur if a message spends too much time on the negative case, if it is too complex, or if the message is threatening.

The American Heritage Dictionary traces the passage of the words bunk (noun), debunk (verb) and debunker (noun) into American English in 1923 as a belated outgrowth of "bunkum", of which the first recorded use was in 1828, apparently related to a poorly received "speech for Buncombe" given by North Carolina representative Felix Walker during the 16th United States Congress (1819–1821).