Ben Stiller's The Secret Life of Walter Mitty is not a completely original story, and is, in fact, a remake of an adaptation of acclaimed humorist James Thurber's famous short story of the same title, which appeared in The New Yorker in March, 1939. The story is in fact the most well known of Thurber's short stories, and was adapted in 1947 into a film starring Danny Kaye.
Thurber's story is very different from both the 1947 and the 2013 film. In the original story, Walter Mitty is a married man who drives to Waterbury, Connecticut with his wife and is overtaken by epic daydreams about various incredible feats, like piloting a U.S. Navy flying boat, performing difficult surgery, and doing the duties of a deadly assassin. The protagonist, Walter Mitty, was considered to be a quintessential "Thurber Man," a somewhat mild-mannered man with a domineering wife, who escapes his difficult marriage through fantasy.
Both the 1947 and 2013 films are quite different from the original, and Thurber was alive to see the first adaptation, of which he did not approve. Indeed, the original short story is considerably darker and more pessimistic than its 1947 comedic interpretation—and certainly darker than its uplifting, inspiring adaptation in 2013. The end of Thurber's short story finds the title character facing a firing squad, and Thurber writes, "He put his shoulders back and his heels together. 'To hell with the handkerchief,' said Walter Mitty scornfully. He took one last drag on his cigarette and snapped it away. Then, with that faint, fleeting smile playing about his lips, he faced the firing squad; erect and motionless, proud and disdainful, Walter Mitty the Undefeated, inscrutable to the last."