Enrico Fermi (1901-1954) was perhaps the greatest physicist of the 20th century. He was a professor in Italy until the late 1930s, when he fled to America in order to escape Mussolini. Fermi was unique in being extraordinary in both experimental and theoretical physics.
In 1926, Fermi discovered the statistical laws known as Fermi statistics, which govern particles (fermions) subject to Pauli's exclusion principle. These particles are different from bosons, which obey Bose-Einstein statistics.
In the mid-1930s, Fermi discovered that one can achieve nuclear transformation by bombarding the element with neutrons. This discovery led to nuclear fission and also the production of new elements beyond the existing Periodic Table. Fermi won the Nobel Prize in Physics in 1938 for his work on the artificial radioactivity produced by neutrons and for nuclear reactions caused by slow neutrons.
After Hahn and Strassmann discovered nuclear fission early in 1939, Fermi discovered the possibility of emission of secondary neutrons and of a chain reaction. He devised a classical series of experiments that generated the first controlled nuclear chain reaction, on a squash court beneath the stands at the University of Chicago's Stagg Field on Dec. 2, 1942. Fermi then played a key role in developing the first atomic bomb.