Enrico Fermi ( September 29 1901 â '' November 28 1954 ) was an Italian physicist who worked on the first nuclear reactor and helped make quantum theory . He also was important to particle physics , and statistical mechanics . Enrico Fermi ( 29 September 1901 â `` 28 November 1954 ) was an Italian-American physicist particularly known for his work on the development of the first nuclear reactor , Chicago Pile-1 , and for his contributions to the development of quantum theory , nuclear and particle physics , and statistical mechanics .