Joseph Rotblat (1908-2005) was a British-naturalized Polish physicist and 1995 Nobel Peace Prize winner.
Rotblat joined British physicist James Chadwick to work on the atomic bomb at Los Alamos in 1944. Rotblat was opposed to using the bomb or using science to develop such a weapon. He left the Manhattan Project on grounds of conscience in late 1944 when it became clear Germany was not close to developing an atomic bomb. Rotblat was not allowed to reenter the United States until 1964 because of an accusation of spying for the Soviet Union.