Rings of Operators
Von Neumann embarked in 1936, with the partial collaboration of F.J. Murray, on the general study of factors classification of von Neumann algebras. The six major papers in which he developed that theory between 1936 and 1940 "rank among the masterpieces of analysis in the twentieth century" (as characterized by Jean Dieudonné in the 7th ed. of the "Complete Dictionary of Scientific Biography"). The direct integral was later introduced in 1949 by John von Neumann. -- Wikipedia entry, John von Neumann.