 He was a senior academic in the field of finance, focusing on derivatives, particularly options, and was probably best known for his contributions to financial theory and practice such as portfolio insurance and the binomial options pricing model (also known as the Cox-Ross-Rubinstein model), as well as his work on discrete time stochastic calculus.Along with fellow Berkeley finance professor Hayne E. Leland, Rubinstein developed the portfolio insurance financial product in 1976.This strategy later became associated with the October 19, 1987, Stock Market Crash (see Black Monday (1987)#Causes).