Szilard, Leo (sĭˈlärd) [key], 1898–1964, American nuclear physicist and biophysicist, born in Hungary. He was educated at the Budapest Institute of Technology and the Univ. of Berlin, receiving a doctorate from the latter in 1922. Working at the Univ. of Chicago with Enrico Fermi, he developed the first self-sustained nuclear reactor based on uranium fission. Szilard was one of the first to realize that nuclear chain reactions could be used in bombs and was instrumental in urging the U.S. government to prepare the first atomic bomb, but he later actively protested nuclear warfare and supported the use of nuclear energy for peaceful purposes.