William Mercer Cook (January 27, 1869 – July 19, 1944), better known as Will Marion Cook, was an American composer, violinist, and choral director. Cook was a student of Antonín Dvořák. In 1919 he took his New York Syncopated Orchestra (Southern Syncopated Orchestra) to England for a command performance for King George V of the United Kingdom, and tour. Cook is probably best known for his popular songs and landmark Broadway musicals, featuring African-American creators, producers, and casts, such as Clorindy, or The Origin of the Cake Walk (1898) and In Dahomey (1903). The latter toured for four years, including in the United Kingdom and United States.

Cook served as musical director of the George Walker-Bert Williams Company, working with the comedy partners on Clorindy, In Dahomey, and several other musical successes.