From the Nobel Foundation:
Pauli was outstanding among the brilliant mid-twentieth century school of physicists. He was recognized as one of the leaders when, barely out of his teens and still a student, he published a masterly exposition of the theory of relativity. His exclusion principle, which is often quoted bearing his name, crystallized the existing knowledge of atomic structure at the time it was postulated and it led to the recognition of the two-valued variable required to characterize the state of an electron. Pauli was the first to recognize the existence of the neutrino, an uncharged and massless particle which carries off energy in radioactive ß-disintegration; this came at the beginning of a great decade, prior to World War II, for his centre of research in theoretical physics at Zurich.
Pauli helped to lay the foundations of the quantum theory of fields and he participated actively in the great advances made in this domain around 1945. Earlier, he had further consolidated field theory by giving proof of the relationship between spin and "statistics" of elementary particles.
Nobel Laureate, Physics Prize, 1945