Knock-knock joke

A knock-knock joke is a type of joke told in the form of a conversation between a person knocking on a door and the person answering it. It always starts with the phrase "Knock, knock!" followed by the question "Who's there?" and ends with a punch line which usually has a pun or some other kind of word play.
The basic format is as follows:
"Joke-Teller:" "Knock Knock!"
"Joke-Hearer:" "Who's there?"
"Teller:" "[a word or phrase]"
"Hearer:" "[the word or phrase the Teller said] who?"
"Teller:" "[the punch line]"
Knock-knock jokes come from "do you know?" jokes in the 1900s and became very popular in the 1930s.
Example.
There are many knock-knock jokes you can make. For example:
"Rocco:" "Knock Knock!"
"Renzo:" "Who's there?"
"Teller:" "New Year!"
"Hearer:" "New Year who?"
"Teller:" "New Year let me out; I want to watch fireworks."
Popular culture.
"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.