Kurt Julian Weill (; German: [vaɪl]; March 2, 1900 – April 3, 1950) was a German-born American composer active from the 1920s in his native country, and in his later years in the United States. He was a leading composer for the stage who was best known for his fruitful collaborations with Bertolt Brecht. With Brecht, he wrote his best-known work, The Threepenny Opera, which includes the ballad "Mack the Knife". Weill held the ideal of writing music that served a socially useful purpose, Gebrauchsmusik. He also wrote several works for the concert hall and a number of works on Jewish themes. He fled Nazi Germany in 1933, arriving in the United States two years later. Settling in New York, he made a substantial contribution to American musical theater through works such as Lady in the Dark and Street Scene.