Tony Cliff (born Yigael Gluckstein; 20 May 1917 – 9 April 2000), was a Trotskyist activist. Born to a Jewish family in Palestine, he moved to Britain in 1947 and by the end of the 1950s had assumed the pen name of Tony Cliff. He was a founding member of the Socialist Review Group, which later became the International Socialists (IS). It eventually became the Socialist Workers Party in 1977. Cliff's major works include State Capitalism in Russia and a three-volume political biography of Lenin.