Caspar Weinberger, who served as defence secretary under former US President Ronald Reagan, has died in hospital aged 88, his family said.
Mr Weinberger was regarded as one of Reagan's closest allies
Mr Weinberger had recently been treated for pneumonia.
He joined the Reagan administration in 1981 and went on to preside over a period of massive military spending.
Mr Weinberger resigned as defence secretary in 1987, amid claims he had been involved in selling arms to Iran to fund pro-US rebels in Nicaragua.
He was pardoned by President George Bush Snr in 1992, weeks before he was to have stood trial over his alleged role in what came to be known as the Iran-Contra affair.
'Cap the Knife'
Mr Weinberger shared with President Reagan a conviction that the Soviet Union was the biggest threat to the US and he oversaw the biggest peacetime increase in defence spending in US history.
His son told Reuters news agency Mr Weinberger should be remembered as "a great American patriot" who helped bring down the Soviet Union.
Former Secretary of State Colin Powell also paid tribute to Mr Weinberger, describing him as "an indefatigable fighter for peace through strength".
During his time in office, Mr Weinberger persuaded Congress to fund the so-called "Star Wars" programme - a system for defending the US against incoming missiles from space and by land.
Mr Weinberger was a divisive figure who clashed with other key players in the Reagan cabinet, but was widely regarded as a close ally of the president himself.
An earlier stint in Washington saw Mr Weinberger managing the federal budget for President Richard Nixon - a period during which he earned the nickname "Cap the Knife" for pushing through a series of cuts.
Friend of Thatcher
Mr Weinberger, the son of immigrants to the US, had trained as a lawyer at Harvard University and served as a soldier during World War II.
After the war, he worked for Ronald Reagan while he was governor of California, gaining a reputation for tight fiscal spending that eventually led to an invitation to work in Nixon's Cabinet in Washington.
Mr Weinberger resigned in 1975 to work for the construction and engineering giant, Bechtel.
He returned to politics to run President Reagan's election campaign, going on to become his defence secretary in 1981.
Mr Weinberger was also an ally of the former UK Prime Minister, Margaret Thatcher, promising her US support during the Falklands War with Argentina in 1982.