Koop served as Surgeon General from November 1981 until October 1989, taking stern and sometimes controversial stands on abortion, AIDS, fatty foods, drugs and cigarettes. In the process, he became one of the most recognizable figures in the Reagan administration, elevating a formerly obscure government position.
His death was announced by Dartmouth's Geisel School of Medicine, where he founded the C. Everett Koop Institute.
The surgeon general, who is the leading U.S. spokesman on public health matters and a presidential adviser, is the head of the Public Health Service Commissioned Corps. Candidates are nominated by the president and must be confirmed by the Senate.
Koop enraged the powerful tobacco industry with his insistence that smoking kills and should be banned.
He spearheaded the drive to make education about AIDS the primary means of preventing the disease, writing a brochure about AIDS that was distributed to millions of American households.
"He saved countless lives through his leadership in confronting the public health crisis that came to be known as AIDS and standing up to powerful special interests like the tobacco companies," U.S. Representative Henry Waxman, a California Democrat, said on Monday.
(Reporting by Paul Thomasch and Corrie MacLaggan; editing by Christopher Wilson and Jackie Frank)