Marcus Samuel Blitzstein, known as Marc Blitzstein (March 2, 1905 – January 22, 1964), was an American composer, lyricist, and librettist. He won national attention in 1937 when his pro-union musical The Cradle Will Rock, directed by Orson Welles, was shut down by the Works Progress Administration. He is known for The Cradle Will Rock and for his Off-Broadway translation/adaptation of The Threepenny Opera by Bertolt Brecht and Kurt Weill.