Daniel Ellsberg (1931-) is an American strategic analyst, best known for leaking a number of volumes of the Pentagon Papers, a classified history of U.S. decisionmaking in Vietnam, which he participated in writing. He has continued in foreign policy analysis and criticism. Recently, he expressed support for Wikileaks.
After college, Ellsberg served in the U.S. Marine Corps for three years, including duty as a rifle platoon leader. He then returned to Havard to earn Ph.D. in Economics at Harvard with the dissertation, "Risk, Ambiguity and Decision. He then went to the RAND Corporation in 1959, consulting to the U.S. government on command and control of nuclear weapons, as well as decisionmaking.
Entering government in 1964, he became Special Assistant to Assistant Secretary of Defense for International Security Affairs John McNaughton, working on Vietnam. Next, he moved to the U.S. State Department 1965 and spent two years at the US Embassy in Saigon, evaluating pacification on the front lines. He worked under Edward Lansdale.
He returned to the Defense Department, to take part in writing a study, commissioned by Secretary of Defense Robert McNamara, to understand U.S. decisionmaking. The group produced a 47-volume report, which has never been released in full.
Ellsberg grew increasingly disenchanted with Johnson Administration policy in the Vietnam War, and leaked a copy to Senator William Fulbright, who took no action. He then gave a copy to the Washington Post, which chose not to publish. Next, he reached an agreement with the New York Times to start publishing excerpts. The U.S. government, learning of the planned publication, sought court action to restrain it; this quickly reached the Supreme Court of the United States in New York Times Co. v. United States.  The press restraint portion went through the cours, starting in New York, but Solicitor General Erwin Griswold] made an emergency petition directly to the Supreme Court, dealing with eleven key secrets. 
He is supportive of Wikileaks, although he observes similarities and differences between the two releases. With respect to similarities, he said
To start is of course that they mostly deal --- not the latest ones, but the Afghan and the Iraq disclosures – deal with wars that are very similar to the war that was exposed in the Pentagon Papers. So many of the issues they reveal are very similar. And also they're both on a scale as to make the pursuit of the source of that very intense and probably successful. In my case I was sure they would know that I was the only, that I was the source of those, and so I expected to be put on trial. I expected, actually, to go to prison for the rest of my life. And the charges did add up to 115 years. I'm very impressed that Bradley Manning, the suspect in this, who has not been proven to be the source yet by the Army but if the Army's --I should say the Pentagon and Army's suspicions are correct then I admire what he did and I feel a great affinity for it, because he did say, allegedly, to the person who turned him in, Adrian Lamo, in a chatlog, that he was prepared, he was ready to go to prison for life or even be executed, he said, in order to share this information with the American people who needed to have it.
Ellsberg saw the situations different in that the Wikileaks releases deal with tactical or operational information, while "the Pentagon Papers were high level, top secret decision papers that showed a great warning, actually, about the escalations that lay ahead, as well as planning for escalations that was being concealed from the American public. Wrongly, I would say, leading them into very dangerous, reckless policies. So these are not the Pentagon Papers. Unfortunately. I wish they were. We need the Pentagon Papers, not only of Afghanistan and Iraq, but as I said, of Yemen, Pakistan and other wars that may lie, or actually covertly …"
- Brad Friedman (1 December 2010), Interview with "Pentagon Papers" Whistleblower Daniel Ellsberg on WikiLeaks, Julian Assange, Hillary Clinton and more..., KPFK
- 403 U.S. 713 (1971)
- The Secret Briefs and the Secret Evidence, National Security Archive, George Washington University