Carnac the Magnificent was a role played by Johnny Carson on The Tonight Show Starring Johnny Carson, and later continued on Late Show with David Letterman, occasionally by Paul Shaffer. One of Carson's most well-known characters, Carnac was a psychic with a large, elaborate turban and a plethora of envelopes, all of which (according to Ed McMahon) were "hermetically sealed" and had been kept in "a mayonnaise jar on Funk and Wagnalls' porch since noon" that day. On the way to his desk after arriving on stage, Carnac would invariably trip and fall (on one memorable occasion, Carson's desk had been replaced with a balsa-wood version, and he smashed right through it).

Carnac's act involved a variation of the magician's billet reading trick: divining the answer to a question putatively written on a card sealed inside one of the envelopes, then opening the envelope to reveal the question. (In many cases, McMahon would repeat the answer after Carnac "divined" it, sometimes resulting in a sneer or other putdown from Carnac.) The resulting jokes were usually either intentionally corny and often involved puns in some way, or involved an unexpected question following a seemingly straightforward answer: or or or

or or Audience reaction played a major role in the skit. If a joke generated a negative response from the audience, Carson/Carnac would cast a comedic curse (e.g., "May a bloated yak change the temperature of your jacuzzi" or "May you walk a mile under a diseased camel") upon them. One memorable curse was "May your only son become the goalie on a nude hockey team". Occasionally the curse would be directed at Ed McMahon if his introduction of Carnac's abilities became too over-the-top. Such "curses" were also standard when the crowd cheered as McMahon announced the final envelope.

The Late Show With David Letterman sometimes pays homage to the skit, with Paul Shaffer as Carnac. Usually this takes place during the Late Show's "Stump the Band" feature, which is also taken from Carson.