Daniel Ellsberg, the whistleblower who exposed years of US top-secret government deceit in the Vietnam War when he leaked the "Pentagon Papers," died on Friday.

He had been diagnosed with inoperable pancreatic cancer in February. The Washington Post reported that Ellsberg wrote an email saying he had refused chemotherapy.

His family said he died at home in Kensington, California. "He was not in pain, and was surrounded by loving family," they said in a statement.

The revelations that Ellsberg made would eventually lead to the Watergate scandal that saw the resignation of former US President Richard Nixon.

What did Daniel Ellsberg leak?

Ellsberg angered the Nixon White House in 1971 when he handed over documents from a top-secret report about US involvement in Vietnam, from 1945 to 1967, to the press.

He had worked on the report after being sent to Saigon for the State Department. His Harvard education as well as serving in the Marine Corps and working at the Pentagon made him a top candidate for the job.

But he had also become disillusioned by the war and realized that the US could not win.

He began copying pages from the 7,000-page report and eventually leaked it to The New York Times, which published a first installment in 1971. This unleashed the fury of the Nixon administration which tried to block further publication.

This eventually resulted in a freedom-of-the-press showdown at the Supreme Court that Nixon lost, marking a turning point for the role of the media in US life and politics.

'Pentagon Papers' stirred outrage in Nixon White House

Ellsberg's experience in Vietnam turned him into a peace activist. He knew that he would most likely end up in jail for leaking the top-secret report had the Supreme Court not ruled in favor of the newspapers.

Influential presidential adviser Henry Kissinger called Ellsberg "the most dangerous man in America who must be stopped at all costs."

Ellsberg went into hiding for two weeks before turning himself in. 

"I did this clearly at my own jeopardy, and I am prepared to answer to all the consequences of this decision," he said at the time.

The anger that he sparked in Nixon's White House — even though the leaked report did not cover his time as president — resulted in G. Gordon Liddy and E. Howard Hunt breaking into the office of Ellsberg's psychiatrist.

The two men would later figure prominently in the Watergate scandal, in which Nixon ordered them to spy on Democrat rivals at a Washington DC hotel.

Ellsberg was charged with espionage, theft and conspiracy, but the judge declared a mistrial after the office break-in was revealed.

'A hero to the end'

Edward Snowden, who would take up the whistleblowing mantel decades later, paid his respects to Ellsberg in a message on Twitter, adding that he had spoken to him just last month.

"He assessed the risk of a nuclear exchange to be escalating beyond 10%," Snowden wrote. "He had hoped to dedicate his final hours to reducing it, for all those he would leave behind. A hero to the end." 

"Daniel was a seeker of truth and a patriotic truth-teller, an antiwar activist, a beloved husband, father, grandfather, and great-grandfather, a dear friend to many, and an inspiration to countless more," Ellsberg's family said of him. "He will be dearly missed by all of us."

Stella Assange, the lawyer and spouse of Julian Assange, called Ellsberg "a generous spirit who will continue to inspire so many of us."

Former Greek Finance Minister Yanis Varoufakis called Ellsberg a personal hero "not only for his brave leaking of the Pentagon Papers, and subsequent championing of Assange and Snowden, but because of his brilliant work as an experimental economist."

Journalist Glenn Greenwald, who published reports based off the documents leaked by Snowden, published a tribute entitled: "We're told never to meet our childhood heroes. Knowing Daniel Ellsberg proved that wrong."

zc, ab/sms (Reuters, AP)