Sir Joseph (Józef) Rotblat KCMG CBE FRS (4 November 1908 – 31 August 2005) was a Polish physicist, a self-described "Pole with a British passport". Rotblat was the only physicist to leave the Manhattan Project (1942–46) on the grounds of conscience. Rotblat's work on nuclear fallout was a major contribution toward the ratification of the 1963 Partial Nuclear Test Ban Treaty.