Much of the time, a movie will only have a single director in a similar way to how most books just have a single writer. This is especially true if a filmmaker wants to be an auteur, which is kind of the cinematic equivalent of being an author, but some books are co-authored, and some movies are co-directed. And a few directing duos are very well-known, especially those who are siblings, like the Coen brothers (Fargo, The Big Lebowski, No Country for Old Men) and the Russo brothers (Avengers: Infinity War and Endgame).