Kurt Weill and Billy Russell are two of the most influential composers of the 20th century. Weill was a German composer who wrote music for the stage, including the famous musical 'The Threepenny Opera'. Russell was an American composer who wrote the musical 'The Fantasticks' and the song 'Aquarius/Let the Sunshine In'. Both composers were known for their innovative and groundbreaking works that pushed the boundaries of musical theater.