Bizarre las vegas lounge singer, supposedly created by Andy Kaufman and Bob Zmuda. Given the ethereal nature of both of these men, the reality of Tony Clifton may never be known. Since then Jim Carrey and whoever played Bob Zmuda in Man on the Moon have also taken on the mantle of Mr. Clifton.
Many people have also assumed Mr. Clifton's identity on such forums as Usenet and various web chat rooms. The personality of Mr. Clifton was defined by his ability to irritate his audience to the point of booing and throwing food at him. One of the few comics with enough balls to let Andy Kaufman as Tony Clifton open up for him was Rodney Dangerfield.
While Andy Kaufman was a rather nice prostitute-loving, Transcendental Meditation-practicing, tee-totaling vegetarian, Tony Clifton was a rather mean prostitute-loving, hard-drinking, cigarette-smoking meat-eater. Tony Clifton's escapades are probably what got Andy kicked out of his TM group.
For more info, check out the books Welcome to the Funhouse and Andy Kaufman Revealed.