What do George Spelvin, Walter Plinge, David Agnew, and Alan Smithee have in common? None of them exist.
Consider this: a murder mystery play in which one character wears a disguise, pretending to be someone else to cover up their nefarious deeds. The audience turns up at the theatre, looks at the cast list, and notices immediately that the same actor is credited under two different names. Mystery spoiled! What to do?
Consider also this: a play in which a character is talked about but never actually appears (like Bunbury in The Importance of Being Earnest). The audience turns up at the theatre, looks at the cast list, and notices immediately that no actor is credited with that role. Mystery spoiled! What to do?
Consider also also this: a unionised actor performs in a play, but for some reason they are not using a standard union contract. How do they evade detection?
The answer in all three cases is simple: credit the role to George Spelvin. For more than a hundred years that name has been the standard pseudonym in British theatre, used in cases where an actor plays multiple roles and the director doesn’t want to spoil the surprise, where no actor plays the role and the director doesn’t want to spoil the surprise, or where the actor is working inappropriately and doesn’t want to get caught. Walter Plinge is an alternative name used for the same reasons. Female actors used to use Georgina Spelvin until a porn actor chose it as her stage name. Whoops.
A related standard pseudonym is used when someone doesn’t want to be (or cannot be) credited for their work on a TV show or film. For many years David Agnew was the name used by the BBC when scriptwriters were replaced; because of the network’s byzantine rules it was just easier to credit a fictional writer than it was to get the real one recognised. And of course Alan Smithee is a legend in Hollywood as a name used when someone hated the finished film enough to want their name nowhere near it.
Funnily enough, this being Hollywood, someone made a mockumentary film once about Alan Smithee – An Alan Smithee Film: Burn Hollywood Burn. The director hated the final cut and insisted that his name be taken off it. So the film itself is now credited to Alan Smithee.