Worked together with Max Born. He also discovered Fermi Statistics, the statistical laws for governing the elementary particles - Fermions - affected by the Pauli Principle. He was also the brain behind the first controlled nuclear chain reaction.

"for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons"
-- Nobel Prize motivation

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source: http://www.nobel.se