Daniel Ellsberg is a former U.S. Marine and military analyst who began a constitutional crisis in 1971 when he released the "Pentagon Papers." The papers comprised the U.S. military's account of activities during the Vietnam War. Ellsberg released top secret documents to The New York Times.
The leak of The Pentagon Papers in 1971 had a monumental impact on the US government's relationships with the American public and with the media, which resounds today.
http://en.wikipedia.org/wiki/Pentagon_Papers