What's the significance of 'In Alphabetical Order' cast listings?
Internet Filmmakers' FAQ
Cast names in a films opening or closing credits are sometimes noted as being listed "In Alphabetical Order". This is usually done for films for one of two reasons (and sometimes both):
Firstly, if the cast includes several big stars who would normally receive top billing in the credits for their movies, listing the names alphabetically resolves any potential arguments over who gets top-billing in the film in question.
Secondly, if the movie uses an ensemble cast, or there is no clear main character, listing the cast credits alphabetically acknowledges that all the actors did similar amounts of work.