Michael P. Mortara, a partner at Goldman Sachs who was instrumental in the founding of the market for mortgage-backed securities, died in November 2000 at his home in Litchfield, Conn. He was 51. The cause was a brain aneurysm, according to Steven Mnuchin, a family friend and a partner at Goldman. At the time of his death, Mr. Mortara was also the president of a Goldman-financed business called GS Ventures. Mr. Mortara was involved in the development of the mortgage-backed securities market when he worked at Salomon Brothers in the 1970's and 1980's with Lewis S. Ranieri, a pioneer in the mortgage-backed securities business. He worked at Salomon from 1974 until 1987, when both he and Mr. Ranieri left after a major management shake-up. He then joined Goldman Sachs to head its mortgage-backed securities division. Mr. Mnuchin said that in this job Mr. Mortara played a role in the development of mortgage-security derivatives, including the interest-only and principal-only forms of a mortgage-backed security. In 1994, Mr. Mortara became co-head of fixed income, currencies and commodities at Goldman Sachs. In September, Mr. Mortara became the president and chief executive of GS Ventures, a venture capital offshoot of Goldman Sachs that was started with $250 million of the firm's capital. Mr. Mortara was born in Torrington, Conn., and received a bachelor of science degree in international economic affairs from the Georgetown University School of Foreign Service in 1971. He received an M.B.A. from the University of Chicago in 1974. He is survived by his wife, Virginia; two sons, Michael P. Jr. and Matthew P.; and his parents, Florence and Nat, of Torrington.