Daniel Ellsberg (April 7, 1931 – June 16, 2023) was an American political activist, economist, and United States military analyst. While employed by the RAND Corporation, he precipitated a national political controversy in 1971 when he released the Pentagon Papers, a top-secret Pentagon study of U.S. government decision-making in relation to the Vietnam War, to The New York Times, The Washington Post, and other newspapers.

In January 1973, Ellsberg was charged under the Espionage Act of 1917 along with other charges of theft and conspiracy, carrying a maximum sentence of 115 years. Because of governmental misconduct and illegal evidence-gathering (committed by the same people who were later involved in the Watergate scandal), and his defense by Leonard Boudin and Harvard Law School professor Charles Nesson, Judge William Matthew Byrne Jr. dismissed all charges against Ellsberg in May 1973.

Ellsberg was awarded the Right Livelihood Award in 2006. He was also known for having formulated an important example in decision theory, the Ellsberg paradox; for his extensive studies on nuclear weapons and nuclear policy; and for voicing support for WikiLeaks, Chelsea Manning, and Edward Snowden. Ellsberg was awarded the 2018 Olof Palme Prize for his "profound humanism and exceptional moral courage". He was a founding member of Veteran Intelligence Professionals for Sanity. Ellsberg died of cancer in 2023.

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