Kurt Julian Weill (March 2, 1900 – April 3, 1950) was a German composer, active from the 1920s, 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 developed productions such as his best-known work The Threepenny Opera, a Marxist critique of capitalism, which included the ballad "Mack the Knife". Weill was a socialist who held the ideal of writing music that served a socially useful purpose. He also wrote a number of works for the concert hall, as well as several Judaism-themed pieces.