Simon died from complications of pulmonary fibrosis, said his daughter, Mary Streep. "His heart valve just gave out."
Named by President Nixon as his choice for deputy secretary of the treasury on Dec, 6, 1972, Simon was sworn into office on Feb. 2, 1973.
Appointed to chair the President's Oil Policy Committee within weeks of his arrival in Washington, Simon had responsibility for the oil import program and quickly became expert on the nation's escalating energy problems.
At the height of the Arab oil embargo in December 1973, Nixon selected Simon as head of the Federal Energy Office. As "energy czar," he instituted a mandatory fuel allocation program and was able to stem the rising tide of public hysteria, without resorting to gasoline rationing, until the embargo was lifted in spring 1974.
Simon continued to serve simultaneously as deputy secretary and head of the FEO until George Shultz's resignation as treasury secretary in April 1974. Nixon nominated Simon to replace him and when Ford assumed the presidency in August 1974, Simon continued in the post.
"He was a man of profound ability, vision, intellect and faith, and he will be missed by all friends of the Nixon legacy," said John H. Taylor, executive director of the Richard Nixon Library & Birthplace Foundation. Simon was founding president of the foundation.
As treasury secretary, Simon headed a 125,000-person department, which collected the nation's taxes, paid its bills, managed its accounts, printed its currency, and minted its coins. During his tenure the $2 bill was reintroduced.
He also had responsibility for the U.S. Customs Service, and the U.S. Secret Service.
When Simon left office at the end of the Ford administration in 1977, he returned to business, serving first as adviser and consultant to such firms as Booz Allen & Hamilton Inc. and Blyth Eastman Dillon & Co. Inc.
Later he formed his own investment firm, the Wesray Corporation. He also wrote two books, both of which became best sellers: A Time for Truth (1978) and A Time for Action" (1980).
Simon was a member of the U.S. Olympic Committee for more than 30 years. A president of the USOC, he oversaw the 1984 Summer Games in Los Angeles. He was inducted into the U.S. Olympic Hall of Fame in 1991.
In 1998, after having already donated an estimated $30 million to various causes, he announced his intention to give away his entire fortune, estimated at $350 million, to charitable organizations, among them AIDS hospices and low-income educational groups.