On Friends, Joey’s imaginary friend was named Maurice.
The answer appears during “The One with the Embryos,” when Rachel and Monica compete against Joey and Chandler in a trivia contest about how well the friends know one another. One of the questions asks for the name of Joey’s childhood imaginary friend, and Rachel correctly answers Maurice.
Joey adds that Maurice was a space cowboy, giving the character an unusually specific backstory. The description is also a musical joke: “The Joker,” Steve Miller Band’s 1973 hit, includes the lines “Some people call me the space cowboy” and “Some people call me Maurice.” Friends uses both ideas together for Joey’s imaginary companion.
The question can be confused with Joey’s many real-life acting roles or with the aliases and characters he invents as an actor. Maurice is different: he is a fictional friend Joey says he had as a child. The canonical quiz answer is simply Maurice, while “Maurice the space cowboy” is the fuller version.