NEW YORK: Arthur M. Schlesinger Jr., the Pulitzer Prize-winning historian and Kennedy insider who helped define mainstream liberalism during the Cold War has died at 89.

Schlesinger suffered a heart attack while dining out with family members on Wednesday night in Manhattan, his son Stephen Schlesinger said. He was taken to New York Downtown Hospital, where he died.

“(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 on Thursday morning, hours after his father’s death. “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.”

Schlesinger was among the most famous historians of his time, and was 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 both a National Book Award and a Pulitzer for “A Thousand Days,” his memoir/chronicle of President John F. Kennedy’s administration. He also won a Pulitzer, in 1946, for “The Age of Jackson,” his landmark chronicle of Andrew Jackson’s administration.

With his bow ties and horn-rimmed glasses, Schlesinger seemed the very image of a reserved, tweedy scholar. He was also an assured member of the so-called Eastern elite.

He was a long-time confidant of the Kennedys, a fellow Harvard man who served in President Kennedy’s administration and was often accused of idealising the family, especially not mentioning the president’s extramarital affairs.

“At no point in my experience did his preoccupation with women -- apart from (his daughter) 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 historians and Democratic officials, he was a kind of professor emeritus, valued for his professional knowledge and for his personal past.

Liberals were wary of Kennedy, but Schlesinger, tired of Stevenson’s dreamy detachment, was drawn to Kennedy’s “cool, measured, intelligent concern.” Over time, he came to embody Schlesinger’s ideal for a head of state: charismatic but not dogmatic; progressive yet practical; a realist, he once observed, brilliantly disguised as a romantic.

Kennedy appointed the Schlesinger a special assistant, an unofficial “court philosopher” of symbolic, if not practical power. The high-minded historian was soon trapped in the tangle of superpower politics: the Bay of Pigs invasion in 1961, the disastrous attempt to overthrow Cuban leader Fidel Castro.—AP