The Mouse That Roared is a 1959 British satirical comedy film on a Ban The Bomb theme, based on Leonard Wibberley's novel The Mouse That Roared (1955). It stars Peter Sellers in three roles: Duchess Gloriana XII; Count Rupert Mountjoy, the Prime Minister; and Tully Bascomb, the military leader; and co-stars Jean Seberg. The film was directed by Jack Arnold, and the screenplay was written by Roger MacDougall and Stanley Mann.

Leonard Patrick O'Connor Wibberley, who also published under the name Patrick O'Connor, among others, was an Irish author who spent most of his life in the United States. Wibberley, who published more than 100 books, is perhaps best known for five satirical novels about an imaginary country Grand Fenwick, particularly The Mouse That Roared (1955).