Hungarian-born American physicist who helped conduct the first sustained nuclear chain reaction and was instrumental in initiating the Manhattan Project for the development of the atomic bomb.

In 1922 Szilard received his Ph.D. from the University of Berlin and joined the staff of the Institute of Theoretical Physics there. When the Nazis came into power in 1933, he went to Vienna and, in 1934, to London, where he joined the physics staff of the medical college of St. Bartholomew's Hospital. There, with the British physicist T.A. Chalmers, Szilard developed the first method of separating isotopes (different nuclear forms of the same element) of artificial radioactive elements. In 1937 Szilard went to the United States and taught at Columbia University.

In 1939 Szilard, Edward Teller, and Eugene Wigner persuaded Albert Einstein to write the famous letter to President Franklin D. Roosevelt advocating the immediate development of an atomic bomb. From 1942 until the end of the war he conducted nuclear research at the University of Chicago, where he helped Enrico Fermi construct the first nuclear reactor. In 1946 he became professor of biophysics at Chicago.

After the atomic bomb was first used, Szilard became an ardent promoter of the peaceful uses of atomic energy and the international control of nuclear weapons, founding the Council for a Livable World. In 1959 he received the Atoms for Peace Award. He published a collection of satirical sketches on the misuse of scientific knowledge entitled The Voice of the Dolphins and Other Stories (1961).