Knopf died of medical complications from a fall in mid-January, his wife, Alice, said.
Knopf was the only child of Alfred Knopf and Blanche Wolf Knopf, giants in the field of publishing. He left his parents' company, Alfred A. Knopf Inc., in 1959 to co-found Atheneum Publishers along with Simon Michael Bessie and Hiram Haydn.
Among Atheneum's releases were Theodore White's "The Making of the President, 1960," Frederic Morton's "The Rothschilds: A Family Portrait" and Edward Albee's play "Who's Afraid of Virginia Woolf." The company published one of Mario Puzo's books but declined to publish "The Godfather."
In later years, the company merged with Charles Scribner's Sons to form Scribner Book Companies. That company was acquired by Macmillan Inc., and Knopf became a senior vice president.
Knopf retired from publishing in 1988.
