A Group ``with bells and whistles.'' It was while studying von Neumann algebras that Jones discovered the amazing and highly unexpected connections with Knot Theory which led to the formulation of the Jones Polynomial.
Iyanaga, S. and Kawada, Y. (Eds.). ``Von Neumann Algebras.'' §430 in
Encyclopedic Dictionary of Mathematics. Cambridge, MA: MIT Press, pp. 1358-1363, 1980.