Founding editor Harold Ross made The New Yorker the great American magazine; Shawn made it, for many years, indispensable. As Ross’s managing editor, Shawn helped him move from a jazz-age sensibility to engagement with the gravest issues of the century. James Thurber, the archetypal New Yorker humorist, felt estranged from the magazine’s new direction; but even he argued that without Shawn, “Ross would never have made the distinguished record he did.” Shawn got Ross to devote an entire issue to John Hersey’s “Hiroshima” in 1946. After Ross died, in 1951, Shawn sponsored new generations of writers with a new array of concerns: from Rachel Carson on the environment and James Baldwin on race to Jonathan Schell on Vietnam and nuclear holocaust.

Shawn sent Hannah Arendt to Israel for the trial of Adolf Eichmann, and Truman Capote to Kansas to cover a gruesome murder: “Eichmann in Jerusalem” and “In Cold Blood” proved magazine journalism could have the intellectual weight of the formal essay and the immediacy of fiction. Shawn’s New Yorker had America’s liveliest film critic (Pauline Kael), most revered baseball writer (Roger Angell), most obsessively dogged reporter (John McPhee, with several runners-up) and smartest short fiction (Cheever, Salinger, Updike, Barthelme). And, always, the best cartoons.

Shawn hardly seemed the man for the job. Born in Chicago of Polish-Jewish parents (the family name was Chon), he’d dropped out of the University of Michigan and worked at the Las Vegas (N.M.) Optic and an obscure news service before going to The New Yorker in 1933 as a miserably paid freelance reporter. In a notorious 1965 article in the New York Herald Tribune, Tom Wolfe ridiculed Shawn’s eccentricities: his shyness, his courtliness, his drab clothes, his phobias. Shawn was hardly a recluse: he threw parties at which he played creditable jazz piano. But even the sympathetic treatment he received in Brendan Gill’s 1975 book, “Here at The New Yorker,” must have made him wince. As a celebrity, he was merely odd; at his “anonymous art,” he was supreme.

The mid-’70s New Yorker, Gill wrote at the time, was “far more nearly a reflection of Shawn’s mind than the magazine of 25 years ago was a reflection of Ross’s.” That, of course, was the rap against Shawn: that he belonged to a more leisurely age (one Updike casual was published 21 years after being bought), was too easily fascinated by such topics as the Law of the Sea Treaty and too soft on chatty writers paid by the word. By 1985 ad revenues were falling, and the magazine was sold to S.I. Newhouse Jr.’s publishing empire. In 1987 Newhouse replaced Shawn with Knopf Editor in Chief Robert Gottlieb; 154 contributors signed a letter urging Gottlieb to refuse. Gottlieb, ironically, proved all too Shawnian, and last summer Newhouse appointed Vanity Fair’s Tina Brown, who set about remaking the magazine as radically as Shawn did 40 years ago. (Last week’s move: making Richard Avedon staff photographer.)

Shawn, meanwhile, became a part-time editor for Farrar Straus & Giroux -one project, Charlayne Hunter-Gault’s memoir, “In My Place,” appeared just last month-and resumed his own writing, largely neglected for a lifetime. “We didn’t ask him, really,” his son, the actor Wallace Shawn, told The New York Times, “but I think it was fiction.” The response suggests both Shawn’s inviolable aura of privacy and the quirky affection that surrounded and protected him. But getting at the real Shawn was always a matter of inference. He could be glimpsed in the dedications of at least 40 books, from Berton Roueche’s true stories of medical detection to Salinger’s “Franny and Zooey,” where he was apostrophized as “lover of the long shot, protector of the unprolific”-that is, a writer’s editor.

His final loyalty, though, was to the reader. “He held to some resolve,” Shawn wrote of Harold Ross, in another bit of cryptic self-portraiture, “never to publish anything, never to have something written, for a hidden reason: to promote somebody or something, to pander to somebody, to build somebody up or tear somebody down, to indulge a personal friendship or animosity, or to propagandize. Everything published in The New Yorker was precisely what it purported to be, was published for its own sake.” This all sounds quaint and quixotic today, when editors and publicist’s cut deals for access to celebrities and when every magazine’s goal is to be the “hot book.” For Mr. Shawn, it was probably time to go.