Albert Einstein

Einstein had already produced relativity and won the Nobel Prize in 1921 by the time Hitler took power. The Nazi regime stripped him of his German citizenship in 1933 while he was lecturing abroad; he never returned. The newly founded Institute for Advanced Study in Princeton offered him a permanent fellowship that year, and he held it for the rest of his life. His most consequential American act was political: the letter he co-signed with Leo Szilard to President Roosevelt on 2 August 1939, warning of the possibility of an atomic bomb, set in motion the policy chain that became the Manhattan Project. Einstein himself was kept out of the project on security grounds. He spent his Princeton years pursuing a unified field theory he never finished.