Gruenberg, Louis (grōˈənbûrg) [key], 1884–1964, American composer, b. Russia; pupil of Busoni. After concert tours as a pianist in Europe and America, he settled in the United States as a composer in 1919. A champion of modern music, he helped found (1923) the League of Composers and was one of the first American composers to incorporate jazz rhythms into works of major dimensions, such as Daniel Jazz (1924) and Jazz Suite (1925). His opera The Emperor Jones, based on O'Neill's play, was presented at the Metropolitan Opera in 1933. From 1940 he composed music for motion pictures.