'Alan Smithee' is a common pseudonym for directors whose film was clearly taken away from her/him and recut heavily against her/his wishes in ways that completely altered the film.

The Directors Guild contract generally does not permit a director to remove her/his name from films. The Directors Guild has been striving for decades to establish the director as the "author" of a film, and part of getting the credit for the successes is taking the blame for the failures. The only exceptions they make are cases in which a film was clearly taken away from a director and recut heavily against her/his wishes in ways that completely altered the film. Directors are required to appeal to the Guild in such cases. If the appeal is successful, their name is replaced by Alan Smithee. That is the only permissible pseudonym for a director. So if you notice a film directed by Alan Smithee, it is certain it is not what its director intended, and likely that it is not any good.
The DGA decided that the name got so much exposure from the film _Alan Smithee Film: Burn Hollywood Burn, An (1997)_ that it was no longer an effective alias. The film Supernova was the first "post-Smithee" film; Smithee's successor is as yet unclear, but one possibility from this film is "Thomas Lee." The name given by directors who disown their films for any reason. "Alan Smithee" is an anagram for "The Alias Men" Directors are still allowed to use other pseudonyms, as are authors, but that pseudonym, such as those used by Nathan Juran and David DeCoteau, are theirs, and a method of detachment rather than disownership.