Enrico Fermi was a titan of twentieth-century physics. Adept in both theory and experiment, the Italian-born American outlined the statistical laws that govern the behavior of particles that abide by the Pauli exclusion principle and developed a theoretical model of the atom when he was only in his mid-twenties. He went on to incorporate the neutral particle (lightheartedly hailed by Fermi as the neutrino, or “little neutral one”) hypothesized by Wolfgang Pauli into a quantitative theory of beta decay, as well as to demonstrate that bombardment of elements with neutrons can generate artificial radioactivity and that slow neutrons produce much stronger nuclear reactions. These latter discoveries paved the way for the invention of nuclear reactors and the atomic bomb.