This photo provided by the John F. Kennedy Presidential Library shows Arthur M. Schlesinger Jr., left, and President Kennedy on July 26, 1962, in the White House Oval Office. Schlesinger died Wednesday after suffering a heart attack while dining with family members in New York. He was 89.

New York ? Arthur M. Schlesinger Jr., the Pulitzer Prize-winning historian and “court philosopher” of the Kennedy administration who remained a proud liberal even as others dared not use the word, has died. He was 89.

Schlesinger was dining with family members Wednesday in Manhattan when he suffered a heart attack, his son Stephen said. He died at New York Downtown Hospital.

Schlesinger was among the most prominent historians of his time, widely respected as learned and readable, with a panoramic vision of American culture and politics. He received a National Book Award for “Robert Kennedy and His Times” and a National Book Award and a Pulitzer for “A Thousand Days,” his memoir/chronicle of President Kennedy’s administration. He also won a Pulitzer, in 1946, for “The Age of Jackson,” his landmark chronicle of Andrew Jackson’s administration.

“(He had) enormous stamina and a kind of energy and drive which most people don’t have, and it kept him going, all the way through his final hours,” Stephen Schlesinger said early Thursday. “He never stopped writing, he never stopped participating in public affairs, he never stopped having his views about politics and his love of this nation.”

With his bow ties and horn-rimmed glasses, Schlesinger seemed the very image of a reserved, tweedy scholar. But he was an assured member of the so-called Eastern elite, friendly with everyone from Mary McCarthy to Katharine Graham and enough of a sport to swim fully clothed in the pool of then-Attorney General Robert Kennedy.

He was a longtime confidant of the Kennedys, a fellow Harvard man who served in President Kennedy’s administration and was often criticized for idealizing the family, especially for not mentioning the president’s extramarital affairs.

“At no point in my experience did his preoccupation with women – apart from Caroline crawling around the Oval Office – interfere with his conduct of the public business,” Schlesinger later wrote.

Liberalism declined in his lifetime to the point where politicians feared using the word, but Schlesinger’s opinions remained liberal, and influential, whether old ones on the “imperial presidency,” or newer ones on the Iraq war. For both historians and Democratic officials, he was a kind of professor emeritus, valued for his professional knowledge and for his personal past.

“Arthur was a trusted friend and loyal adviser to President Kennedy, and a wonderful friend to me and to all of us in the Kennedy family,” Sen. Edward M. Kennedy, D-Mass., said in a statement. “I will miss him terribly, but his contributions to this country will live on.”

A native of Columbus, Ohio, and the son of a prominent historian, he was born Arthur Bancroft Schlesinger Jr., but later gave himself his father’s middle name, Meier. Family friends included James Thurber, historian Charles A. Beard and future Supreme Court justice Felix Frankfurter.

His time in government was brief. Kennedy was assassinated in 1963, and the historian soon left the administration of his successor, Lyndon Johnson. (“With Kennedy gone, it was no longer exhilarating,” Schlesinger explained). Schlesinger then supported Robert Kennedy’s brief, tragic 1968 campaign.

In 1998, Schlesinger opposed Republican-led attempts to have President Clinton removed from office, and he later criticized President George W. Bush for his doctrine of “preventive war,” saying “I think the whole notion of America as the world’s judge, jury and executioner is a tragically mistaken notion.”

Schlesinger had six children – four from his first marriage, to the author Marian Cannon, and two from his second, to Alexandra Emmet.