I just tripped over this in an old copy of Schott's Almanac (I'm sooo busy!) and it kind of amused me. You probably know it already but I can't help that. I paraphrase:
Alan Smithee is a highly prolific Hollywood director who doesn't exist. It is, or was, the pseudonym granted by Directors Guild of America to directors who, for reasons of artistic integrity or whatever, don't want their real names on the credits of a film. So Smithee has probably made some pretty damn bad movies.
In 1997, the director Arthur Hiller made a film about a director who is actually called Alan Smithee in real life, and wants his name removed from a turkey he's made. On release of his (real) film, Hiller was permitted by the DGA to have his own name replaced by Alan Smithee.