One by one, he photocopied thousands of top-secret documents that he hoped would end a long and costly conflict.
Known as the Pentagon Papers, the documents were part of a classified study that showed the extent of American involvement in the Vietnam War.
Mr Ellsberg famously leaked the study to newspapers in 1971 before facing espionage charges that were ultimately dismissed.
While the Pentagon Papers left a lasting legacy, they weren’t the only documents Mr Ellsberg got his hands on.
At the same time, Mr Ellsberg copied another classified study that showed how seriously American military chiefs took the threat of nuclear war during the Taiwan crisis of 1958.
For 50 years, the study went virtually unnoticed until 2017, when Mr Ellsberg published the full document online, which was highlighted by the New York Times newspaper last month.
In theory, Mr Ellsberg’s disclosure could put him at risk of prosecution on the same charges he faced for leaking the Pentagon Papers.
