Arturo Toscanini
Toscanini was often criticized for not performing much American music and contemporary music (music by living composers).  However, in 1938, he conducted the world premieres of two orchestral works by Samuel Barber, Adagio for Strings and Essay for Orchestra (Barber)|Essay for Orchestra.  In 1945, he led the orchestra in Carnegie Hall recording sessions of American music including An American in Paris by George Gershwin.  He also conducted broadcast performances of Copland's El Salon Mexico and Gershwin's Rhapsody in Blue with soloists Earl Wild and Benny Goodman and Concerto in F with pianist Oscar Levant, as well as music by other American composers, including two marches of John Philip Sousa.