The War with Grandpa is a 2020 American family comedy film directed by Tim Hill, from a screenplay by Tom J. Astle and Matt Ember, based upon the novel of the same name by Robert Kimmel Smith. The film is about a young boy named Peter (Oakes Fegley) who fights in a prank war with his grandfather (Robert De Niro) to get his grandfather to move out of his room after he moves in with his family. Uma Thurman, Rob Riggle, Laura Marano, Cheech Marin, Jane Seymour, and Christopher Walken also star.