Donald Thomas Regan was born in 1918 in Cambridge, Massachusetts. He earned a B.A. from Harvard University in 1940 and attended Harvard Law School before leaving his studies during World War II for service in the Marines.

After seeing action in the Pacific, Regan left the military in 1946 with the rank of reserve lieutenant colonel. He returned to the United States and joined Merrill Lynch, Pierce, Fenner & Smith, a Wall Street investment company, as an executive trainee; by 1960, he was director of the company’s administrative division, and by 1971, he had become the firm’s chairman and chief executive officer.

In 1981, President Ronald Reagan tapped Regan to become his secretary of the treasury, a post Regan held until 1985. During his tenure, Regan helped implement the President’s economic policies, which included tax cuts, budget cuts, and increased spending on national defense. In 1985, Regan swapped positions with Chief of Staff James Baker.

Clashes with First Lady Nancy Reagan and the emergence of the Iran-Contra scandal led Regan to resign from the Reagan administration. He retired to Virginia and wrote his memoirs.