Gregory Breit was an American physicist. He was born on July 14, 1899 in Mykolaiv, Ukraine. He received his entire university education from Johns Hopkins University, earning a Ph.D. in physics at the age of 22 (1921). Highly esteemed as a theoretical physicist, Breit joined the Manhattan Project in 1942 in Chicago and began making designs for an atomic bomb. In 1968, President Johnson presented him with a National Medal of Science for contributions to the first atom smashers and ordnance development. In 1964, he received the Franklin Medal for work in nuclear physics. During his long career Breit taught at the University of Minnesota (1923–24), was a physicist in the department of terrestrial magnetism at the Carnegie Institution for Science (1924–29), and was a professor at New York University (1929–34), the University of Wisconsin (1934–47), Yale University (1947–68), and the State University of New York at Buffalo (1968–73). He was a member of the National Academy of Sciences (elected 1939) and of the American Academy of Arts and Sciences (elected 1951).