Wolfgang Ernst Pauli (1900-1958), an Austrian-American physicist noted for his work on quantum mechanics. In 1924, Pauli proposed a new quantum degree of freedom to resolve inconsistencies between observed molecular spectra and the developing theory of quantum mechanics. He formulated the Pauli exclusion principle in 1925, perhaps his most important work, which stated that no two electrons could exist in the same quantum state. He was the first to recognize the existence of the neutrino, an uncharged and massless particle that carries off energy in radioactive disintegration. Pauli was awarded the Nobel Prize in Physics in 1945.