Walter Mitty is a fictional character in James Thurber's short story The Secret Life of Walter Mitty, published in 1941. Mitty is a meek, mild man with a vivid fantasy life: in a few dozen paragraphs he imagines himself a wartime pilot, an emergency-room surgeon, and a devil-may-care killer. The term now appears in dictionaries to describe a person who lives a fantasy life.

A film version of the story was released in 1947 starring Danny Kaye and directed by Norman McLeod.

In 1977, former British prime minister Harold Wilson sued an unofficial biographer for a work subtitled "the Yorkshire Walter Mitty".

In 2003, a U.K government official publicly apologised for referring to the late David Kelly as "a Walter Mitty character".