Alexander Haig, a former NATO commander and a top official in three Republican administrations, died on Saturday, Fox News reported, citing Haig's family.
Haig, 85, had been hospitalised for nearly a month in Johns Hopkins Hospital in Baltimore, Maryland, from complications related to an infection.
Haig served in the administrations of presidents Richard Nixon, Gerald Ford and Ronald Reagan, and was also supreme allied commander of NATO forces in Europe during the late 1970s. He was White House chief of staff when Nixon resigned over the Watergate scandal and served as secretary of state under Reagan.
Haig served in the US military in Japan starting in 1947, and later served on General Douglas MacArthur's staff in Japan during the 1950-53 Korean War.