Knock, knock! Who's there?
Porter:Macbeth Act 2, scene 3, 1–8
Here's a knocking indeed! If a man were porter of Hell Gate,
he should have old turning the key. [Knock] Knock, knock,
knock! Who's there, i' th' name of Belzebub? . . . [Knock] Knock,
knock! Who's there, in th' other devil's name?
On August 19, 1936, the entertainment industry trade magazine Variety reported that a "'Knock Knock' craze" was sweeping America. A few months later, on the evening of November 14, a radio performer named Wee Georgie Wood set England afire with "Knock Knock" jokes. From its disreputable beginnings—as a formula for tasteless puns—the "Knock Knock" joke emerged to take the English-speaking world by storm. In these days of decline, "Knock, knock! Who's there?" calls forth yawns more often than giggles, and chiming "Knock, knock!" is merely a cute substitute for actually knocking on someone's door.
Although there's no direct line of descent, it's possible that the birth of "Knock Knock" jokes in the dim recesses of our century owes more than a little to the famous "porter scene" in Macbeth. The clownish porter tends the gate at Macbeth's castle, where that notable thane has just successfully murdered the king of Scotland. In the previous scene, in which Macbeth and his wife complete the deed, the knocking sounds that eventually rouse the porter scare the conspiratorial couple out of their wits: knocking is the sound that crystallizes their guilt. The porter's joking reference to "Hell Gate" has, then, some resonance: Macbeth's castle is and will remain the diabolical duo's headquarters, and the scene of numerous hideous crimes. The joke also refers obliquely to an earlier dramatic form in which Hell Gate was an actual prop, and in which the drama of temptation, sin, salvation, and damnation was materialized to edify the common people, Macbeth supplies the tradition with psychological depth.