NEW YORK — Daniel Ellsberg, the history-making whistleblower who by leaking the Pentagon Papers revealed longtime government doubts and deceit about the Vietnam War and inspired acts of retaliation by President Richard Nixon that helped lead to his resignation, has died. He was 92.

Ellsberg, whose actions led to a landmark First Amendment ruling by the Supreme Court, had disclosed in February that he was terminally ill with pancreatic cancer. His family announced his death Friday morning in a letter released by a spokeswoman, Julia Pacetti.

“He was not in pain, and was surrounded by loving family,” the letter reads in part. “Thank you, everyone, for your outpouring of love, appreciation and well-wishes to Dan in the previous months. It all warmed his heart at the end of his life.”

Until the early 1970s, when he disclosed that he was the source for the stunning media reports on the 47-volume, 7,000-page Defense Department study of the U.S. role in Indochina, Ellsberg was a well-placed member of the government-military elite. He was a Harvard graduate and self-defined “cold warrior” who served as a private and government consultant on Vietnam throughout the 1960s, risked his life on the battlefield, received the highest security clearances and came to be trusted by officials in Democratic and Republican administrations.

He was especially valued, he would later note, for his “talent for discretion.”

But like millions of other Americans, in and out of government, he had turned against the yearslong war in Vietnam, the government’s claims that the battle was winnable and that a victory for the North Vietnamese over the U.S.-backed South would lead to the spread of communism throughout the region. Unlike so many other war opponents, he was in a special position to make a difference.

“An entire generation of Vietnam-era insiders had become just as disillusioned as I with a war they saw as hopeless and interminable,” he wrote in his 2002 memoir, “Secrets: A Memoir of Vietnam and the Pentagon Papers.” “By 1968, if not earlier, they all wanted, as I did, to see us out of this war.”

The Pentagon Papers had been commissioned in 1967 by then-Defense Secretary Robert S. McNamara, a leading public advocate of the war who wanted to leave behind a comprehensive history of the U.S. and Vietnam and to help his successors avoid the kinds of mistakes he would only admit to long after. The papers covered more than 20 years, from France’s failed efforts at colonization in the 1940s and 1950s to the growing involvement of the U.S., including the bombing raids and deployment of hundreds of thousands of ground troops during Lyndon Johnson’s administration. Ellsberg was among those asked to work on the study, focusing on 1961, when the newly-elected President John F. Kennedy began adding advisers and support units.