The knock-knock joke is a "call and response" joke, usually ending with a pun. The teller of the joke calls "Knock, knock!", the other person respond "Who's there?" and the teller gives a name (such as "Al"). The other person then responds by asking the caller's surname ("Al who?"), to which the joker teller delivers a pun ("Al be seeing you!").
History
Writing in the Oakland Tribune, Merely McEvoy recalled a style of joke from around 1900 where a person would ask a question such as "Do you know Arthur?", the unsuspecting listener responding with "Arthur who?" and the joke teller answering "Arthurmometer!"
A variation of the format in the form of a children's game was described in 1929. In the game of Buff, a child with a stick thumps it on the ground, and the dialogue ensues:
Knock, knock! Who's there? Buff. What says Buff? Buff says Buff to all his men, And I say Buff to you again.In 1936, the standard knock-knock joke format was used in a newspaper advertisement. That joke was:
Knock, knock! Who's there? Rufus. Rufus who? Rufus the most important part of your house.A 1936 Associated Press newspaper article said that "What's This?" had given way to "Knock Knock!" as a favorite parlor game. The article also said that "knock knock" seemed to be an outgrowth of making up sentences with difficult words, an old parlor favorite. A popular joke of 1936 was "Knock knock. Who's there? Edward Rex. Edward Rex who? Edward wrecks the Coronation." Fred Allen's December 30, 1936 radio broadcast included a humorous wrapup of the year's least important events, including a supposed interview with the man who "invented a negative craze" on April 1: "Ramrod Dank... the first man to coin a Knock Knock."
"Knock knock" was the catchphrase of music hall performer Wee Georgie Wood, who was recorded in 1936 saying it in a radio play, but he simply used the words as a reference to his surname and did not use it as part of the well-known joke formula. The format was well known in the UK and US in the 1950s and 1960s before falling out of favor. It then enjoyed a renaissance after the jokes became a regular part of the badinage on Rowan & Martin's Laugh-In.
In France and Quebec, the punchline is sometimes a pun on the title of a popular song, allowing the last answer to be sung:
Toc Toc! (Knock knock!) Qui est là? (Who's there?) Sheila. Sheila qui? (Sheila who?) Sheila lutte finale ... [A pun on "c'est la lutte finale" (it's the final struggle), the first line of the chorus of The Internationale.]