Walter Mitty appears in the short story The Secret Life of Walter Mitty, written by humorist James Thurber and published in The New Yorker in 1939. Mitty is a meek and henpecked husband who daydreams of being a daring surgeon, heroic pilot and dashing naval commander. ("Throw on the power lights! Rev her up to 8500! We're going through!") Thurber's story was a mere 2100 words long, but the character struck a chord and "Walter Mitty" has become popular shorthand for any timid soul who dreams of a more dashing life. The Secret Life of Walter Mitty was made into a 1947 film with Danny Kaye as Mitty.

Extra credit: A 21st-century feature film based on the story has been rumored for years (with Jim Carrey, Mike Myers and others allegedly set to star as Mitty) but has yet to be produced... It's not true that the cartoon dog Snoopy was originally based on Mitty, but the official Peanuts website does call Snoopy "an extroverted beagle with a Walter Mitty complex."