Regan blamed former first lady Nancy Reagan for his abrupt ouster as the president's chief of staff in February 1987 and got even the next year in a famous tell-all memoir in which he revealed that Mrs. Reagan had consulted extensively with San Francisco astrologer Joan Quigley.
"Virtually every major move and decision the Reagans made during my time as White House chief of staff was cleared in advance with a woman in San Francisco who drew up horoscopes," Regan wrote in his book, "For the Record: From Wall Street to Washington."
Regan died early Tuesday morning at a hospital near his home in Williamsburg, Va., a hospital spokeswoman said. He had been admitted to the hospital on Sunday.
"He leaves behind a lifetime of service and achievement, in both the private and public sector," President Bush said Tuesday evening. "He served his country with distinction."
The chairman of brokerage giant Merrill Lynch before his selection as Reagan's first Treasury secretary, Regan won praise as chief spokesman for Reagan's landmark 1981 tax cut, at the time the largest in history.
Regan suggested a famous job swap at the beginning of Reagan's second term in which he became White House chief of staff and James A. Baker III, Reagan's first chief of staff, became Treasury secretary.
It soon became apparent, however, that Regan lacked the deft touch with Congress and the media that Baker had enjoyed and he also quickly ran afoul of Nancy Reagan, who fumed at what she viewed as Regan's imperious management style.
She took particular umbrage at a famous Regan quote in 1986, when the chief of staff took credit for repairing the damage from a summit meeting Reagan had held in Iceland with Soviet leader Mikhail Gorbachev. "Some of us are like a shovel brigade that follow a parade down Main Street cleaning up," Regan said of the summit meeting. "We took Reykjavik and turned what was really a sour situation into something that turned out pretty well."
In her own memoir, Mrs. Reagan said that Regan had "acted as if he were the president" and deserved to be fired because the Iran-Contra affair had occurred on his watch.
Regan always claimed that he had been made a scapegoat for Iran-Contra, the scheme overseen by National Security aide Oliver North to sell arms to Iran while seeking freedom for American hostages being held in the Middle East. Some of the proceeds of the arms sales were diverted to the Contra rebels, who in the 1980s were fighting the Soviet-backed government of Nicaragua's Daniel Ortega.
A presidential board of inquiry headed by former Sen. John Tower issued a report in February 1987 that said Regan was responsible "for the chaos that descended upon the White House." Regan was forced to resign later that month and was replaced as chief of staff by former Republican Senate Majority Leader Howard Baker.
It took Regan only 15 months to gain a measure of retribution with a best-selling memoir and its revelations of Mrs. Reagan's astrologer. Mrs. Reagan in her book said Regan had betrayed a confidential relationship she had with the astrologer and accused him of twisting it "to seek his revenge on Ronnie and me."
In a statement released on Tuesday, Mrs. Reagan said she was saddened to learn of Regan's death and said he had "served this country with great distinction."
Other than the controversy stirred up by his book, Regan chose to live quietly in retirement, taking up landscape painting.
"After Wall Street and the government, I decided there had to be more to life than the stock market, golf and drinking," he said.
Current Treasury Secretary John W. Snow praised Regan as "a great Treasury secretary and an innovative leader of the American business community." Timothy J. Sullivan, the president of the College of William and Mary, praised Regan for taking time to teach classes and becoming a "generous supporter" of the Williamsburg, Va., university.
Before coming to Washington with the Reagan administration, Regan had spent more than three decades at Merrill Lynch, rising through the ranks from stockbroker to head of the firm from 1971 until 1981.
Regan was born in Cambridge, Mass., in 1918 to a Boston policeman who was among many fired the next year by Gov. Calvin Coolidge for refusing to replace striking policemen - an action that helped propel Coolidge onto the national stage and later the presidency.
Regan, who took pride in his outspoken style, wrote in his memoir that he was expelled from kindergarten after telling his teacher that she was a poor manager and recommending that she "reorganize the class along more sensible lines devised by myself."
Regan went on to graduate from Harvard University and join the Marine Corps where he fought in a number of Pacific island battles against the Japanese in World War II.
Regan is survived by his wife of 60 years, Ann Buchanan Regan of Williamsburg, Va., and four children: Donna Regan Lefeve of Alexandria, Va., Donald T. "Tom" Regan Jr. of Sarasota, Fla., Richard W. Regan of Denver and Diane Regan Doniger of Santa Fe, N.M.
He also is survived by nine grandchildren.
By Martin Crutsinger