William Manchester, who has died aged 82, was an American reporter, foreign correspondent and prolific popular historian, whose work sold in enviable quantities. His controversial account of the assassination of President Kennedy in 1963, The Death Of A President (1967), sold 1.6m copies, and he wrote more than a dozen other books, including two volumes of a three-volume biography of Winston Churchill, which he called The Last Lion.
Manchester had met the young John Kennedy in the south Pacific when they were both recovering from war wounds, and, in 1962, wrote an all but hagiographical work, Portrait Of A President, about him. It was thus no surprise that he was chosen by the president's widow Jacqueline and his brother Robert to write an account of the assassination that would fix Kennedy's image as a national hero and martyr, at the same time contrasting him unfavourably with his successor, Lyndon Johnson.
Manchester obliged to such effect that his book eventually backfired and damaged Robert Kennedy more than Johnson.
He had originally planned to open the book with a highly drawn account of Kennedy being bullied by Johnson into shooting a deer on his Texas ranch. (Johnson indignantly pointed out later that Kennedy had actually insisted on shooting two deer, one more than etiquette required.) But although he was persuaded by his editor to tone down the episode and move it 150 pages into the narrative, Manchester still portrayed Kennedy as "looking into the face of the life he was about to take", and being traumatised by the experience.
More generally, Manchester portrayed Johnson as coarse, crass and boorish. He confessed in a letter to Jacqueline Kennedy that Johnson always reminded him "of somebody in a grade-D movie on the late show". His own publisher described the book as "in part, gratuitously and tastelessly insulting to Johnson", and the distinguished Harvard historian, Arthur Schlesinger, whose own biography of Kennedy was widely felt to be somewhat over-friendly to its subject, called Manchester's book "long, deeply felt, greatly overwritten".
Even Jacqueline Kennedy, who hated the book and offered a magazine $1m to kill its serialisation, said publicly that Manchester had made "inaccurate and unfair references" to Johnson and others, though she did not name them.
Lyndon Johnson saw The Death Of A President as simply part of a conspiracy to discredit him, masterminded by Robert Kennedy, whom he disliked even more than he feared. The historian of the feud, Jeff Shesol, however, recorded that Johnson's relatively reticent public response to the book worked; as a result of the row, 20% of Americans thought less of Robert Kennedy as a result.
Manchester certainly possessed some of the requisite virtues for a popular historian. He was phenomenally industrious as a researcher, and had a command of powerful, emotional narrative. Above all, he was a hero worshipper. His heroes - mostly of a manly and conservative stamp, including General Douglas MacArthur and HL Mencken, as well as Kennedy and Churchill - were those of the mass-market public, which rewarded him with deep affection, as well as royalties.
Manchester himself grew up in Springfield, Massachusetts, in the twelfth generation of a family which had emigrated to the colony from 17th-century England. His first ambition was to shine on the stage, but an attempt to ambush Orson Welles, when the great actor and producer visited Manchester's high school, backfired. When Manchester told Welles that he was the president of the Springfield Classical high school dramatic society, Welles's eyes bulged, his jaw dropped and he feigned awe in the voice that had created Citizen Kane.
In later life, Manchester liked to relate that his literary ambitions had been fired by the chance purchase of the collected works of Shakespeare (all but Macbeth, added later) for $4.10.
The Manchesters were a soldierly clan. Eighteen of them were said to have served under George Washington, and the historian's father was decorated for service in the first world war. In 1942, the young William volunteered for the US marines, and was accepted only after he had stuffed himself with milk and bananas to the point of vomiting to reach the minimum weight.
Wounded in the knee at Okinawa, he left hospital, hitchhiked to the front and joined his regiment in a fierce, nine-day battle just a few weeks before the dropping of the atomic bomb ended the war. Blown up by a mortar round, he was left for dead for four hours, until an orderly saw he was still alive and gave him two shots of morphine. His bravery won him the Navy Cross, the Silver Star and two Purple Hearts.
When Manchester recovered from his wounds, he took a job as a copyboy on the Daily Oklahoman at $16 a week. He was so keen to get his work into the paper that he got into serious trouble for borrowing the bylines of star reporters.
After graduating from the University of Massachusetts in 1946, and taking a master's degree from the University of Missouri, he was given a job on the Baltimore Sun by HL Mencken, a compliment he later returned with an admiring biography. He left journalism in 1955 to take up a job at Wesleyan University, a small college in Connecticut with a tradition of inviting talented writers to live on campus. There, he poured out book after book.
In 1979, having finished his MacArthur biography, Manchester went back to Okinawa, a journey that led to what many believe was the best, and certainly the most deeply personal, of all his books, Goodbye Darkness (1980), in which he evoked the horror and chaos of combat and the friendships of frightened young marines.
Critics disagreed about the merits of the first two volumes of his Churchill biography. Time magazine called the second volume, alone, one of the best non-fiction books of the decade, while the New York Review of Books dismissed it as "hackneyed, coarse and hyperbolic". But Manchester's readers loved them; some 400,000 people purchased each volume, and one at least called him "America's greatest living historian".
His last book was a popular history of the Renaissance and the Reformation, entitled A World Lit Only By Fire (1992), and that, too, was immensely popular, though largely ignored by professional historians.
It was thus a disappointment to his army of readers - as well as a personal tragedy - when, early in 2002, Manchester had to admit that, after two strokes, he would never finish the third volume of the Churchill trilogy, of which he had written more than 200 pages. He could still read and absorb information, he said, but could no longer find the words that had tumbled on to the page in their hundreds of thousands. He told a reporter: "I can't put things together. I can't make the connections. Language for me came as easily as breathing for 50 years, and I can't do it anymore. "
Manchester's wife, Julia Brown Marshall, whom he married in 1948, died in 1998. He is survived by their son and two daughters.
· William Manchester, historian and journalist, born April 1 1922; died June 1 2004
