Klaus Fuchs

German-born British physicist who provided the Soviets with nuclear secrets from the Manhattan Project. A member of the German Communist Party, Fuchs was forced to flee Nazi Germany in 1933. Despite his communist background, and despite the fact that this background led to his expulsion from Britain in 1940, Fuchs was recruited to join the Manhattan Project in 1941. He proceeded to keep the Soviets informed on theproject's progress until the end of the war. Fuch's provided details about how Manhattan Project scientists separated uranium-235 -- the fuel for the atomic bomb -- from uranium-238. Debate remains over how much he helped the Soviet nuclear weapons program, but it is believed he saved them at least one year's work in their own program to develop the atomic bomb.

Fuchs' activities were finally detected and he was arrested in 1950. He confessed and was sentenced to 14 years in prison. Nine years later he was released on good behavior and moved to communist East Germany . There, he was rewarded with the directorship of a nuclear research institute. He died in 1988.