Birtwistle, Sir Harrison (1934-...), an English composer, became a leader in avant-garde (experimental and unconventional) music in the United Kingdom. He is probably best known for his theater pieces. He also composed orchestral pieces, chamber works, brass band compositions, and instrumental and vocal works. Birtwistle's music has been described as lyrical and strongly poetic, distinguished by a characteristic use of repeated thematic fragments as a basis for composition.