Rex Todhunter Stout (; December 1, 1886–October 27, 1975) was an American writer noted for his detective fiction. His best-known characters are the detective Nero Wolfe and his assistant Archie Goodwin, who were featured in 33 novels and 39 novellas or short stories between 1934 and 1975.

In 1959, Stout received the Mystery Writers of America's Grand Master Award. The Nero Wolfe corpus was nominated Best Mystery Series of the Century at Bouchercon XXXI, the world's largest mystery convention, and Rex Stout was nominated as Best Mystery Writer of the Century.

In addition to writing fiction, Stout was a prominent public intellectual for decades. Stout was active in the early years of the American Civil Liberties Union and a founder of the Vanguard Press. He served as head of the Writers' War Board during World War II, became a radio celebrity through his numerous broadcasts, and was later active in promoting world federalism. He was the long-time president of the Authors Guild and sought to benefit authors by lobbying for improvement of authors' rights under the copyright laws. He also served a term as president of the Mystery Writers of America in 1959.