Daniel Ellsberg was a well-known journalist and activist recognized for his opposition to the Vietnam War. He gained notoriety for leaking the Pentagon Papers in 1971, which revealed that the U.S. government had misled the public about the war's progress and decision-making processes. His actions sparked widespread debate about government transparency and civil disobedience. Ellsberg’s bravery in exposing the truth not only influenced public opinion against the Vietnam War but also established him as a key figure in American journalism.