Arthur Gelb, right, with A.M. Rosenthal at the New York Times in 1967. (The New York Times)

Arthur Gelb, a key editor at the New York Times whose ferocious appetite for cultural news and ambitious approach to metropolitan coverage vastly broadened the newspaper’s scope and who co-wrote the first definitive biography of Nobel Prize-winning playwright Eugene O’Neill, died May 20 in Manhattan. He was 90.

The cause was complications from a stroke, said a spokeswoman for the Metropolitan Opera in New York, where Mr. Gelb’s son Peter is general manager.

The son of Jewish immigrants from Eastern Europe, Mr. Gelb grew up in New York and developed two passions as a teenager: theater and journalism. He joined the Times in 1944 as a $16-a-week copy boy and, within weeks, started an in-house newsletter that he figured would provide access to editors who could advance his career prospects.

The venture marked the beginning of his ascent to the heights of journalistic influence.

As a culture writer in the late 1950s and early 1960s, Mr. Gelb highlighted little-known entertainers including Barbra Strei­sand, Woody Allen, Dick Gregory, Lenny Bruce and Phyllis Diller, novice playwrights such as Edward Albee, and the theater impresario Joseph Papp.

Mr. Gelb was deputized in 1963 by the new metropolitan editor, A.M. “Abe” Rosenthal, who was back in New York after many years as a foreign correspondent. “Abe-’n’-Artie,” as they were dubbed, shared a background as first-generation Americans. The two also had an aggressive distaste for the dull and dutiful.

Reporter and then op-ed columnist Maureen Dowd once depicted Mr. Gelb, who had stood 6-foot-2, pacing the newsroom “with eyes going like a slot machine and arms like airplane propellers.”

Not every story idea he suggested was a gem, he admitted, but cumulatively he was credited with transforming the paper’s predictable, not particularly crusading local coverageinto enterprise journalism about city life. He also encouraged literary flair in a newspaper long derided as the “Gray Lady.”

Mr. Gelb was a driving force behind the 1965 front-page exclusive report that Dan Burros, the grand dragon of the New York State Ku Klux Klan and a former American Nazi Party official, had been born and raised Jewish.

He pushed the reporter, Mc­Candlish Phillips, to document Burros’s Hebrew school student record and bar mitzvah. In the wake of the publicity, Burros fatally shot himself. The story, and the story behind the story, became canonical in journalism-school studies.

In 1967, Mr. Gelb succeeded Rosenthal (later the top newsroom executive) as metropolitan editor and continued leading distinguished coverage of the city’s economic, social and racial tremors.

One of the biggest stories to unfold on Mr. Gelb’s watch was a series of allegations by city police officer Frank Serpico in 1970 about systemic corruption in the force. The malfeasance, he claimed, included cops accepting payoffs from criminals, dealing drugs and harassing witnesses.

Initially, Mr. Gelb was skeptical of Serpico, whose undercover appearance did not inspire confidence. “He had long hair and a beard — before reporters had long hair and beards — and I thought he was a nut,” Mr. Gelb told Newsweek. But he gradually became convinced of Serpico’s credibility and pushed for front-page coverage.

In response to the stories, Mayor John V. Lindsay formed a commission that led to reforms in the police force.

In addition to his role as metropolitan editor, Mr. Gelb oversaw the paper’s daily cultural report and hired many of the marquee critics of the day, including Mel Gussow on theater, Anna Kissel­goff on dance and Vincent Canby on film.

When the pornographic film “Deep Throat” became in 1972 an unexpected phenomenon — and then the subject of an obscenity trial — Mr. Gelb and a handful of buttoned-down Times staffers slinked into a matinee showing at a nearby theater to obtain what he described as “a clearer understanding of the forthcoming trial story.”

Halfway through, Mr. Gelb wrote in his 2003 memoir, “City Room,” the theater manager made an announcement over the loudspeaker: “Mr. Arthur Gelb, metropolitan editor of the New York Times, is wanted back at his office.”

It was a prank by a colleague who phoned the theater, helpfully advising that “Mr. Gelb is hard of hearing so be sure to page him nice and loud.”

As assistant and then deputy managing editor starting in the late 1970s, Mr. Gelb was considered the principal architect of the Weekend, Living, Home, Sports Monday and Science Times sections. They became highly profitable and circulation-boosting undertakings amid competition from television and criticism that the paper had become too dense for workaday readers.

Mr. Gelb insisted on rigorously reported and engaging editorial content in the new cultural sections — a rarity in an era when lifestyle pages were largely dismissed as junky advertising vehicles. Many other newspapers copied the format.

Mr. Gelb was named managing editor in 1986 and left the newsroom three years later at the paper’s mandatory retirement age. He then served as president of the New York Times Company Foundation and directed the Times college scholarship program.

Alex S. Jones, a Pulitzer Prize-winning Times reporter who is now director of the Shorenstein Center on Media, Politics and Public Policy at the Harvard Kennedy School, likened Mr. Gelb’s energetic mind to “a sword being sharpened on a grinding wheel that shoots off sparks like a shower.”

Some reporters learned to dodge the sparks — worried that one of his brainstorms would tie them up for days.

In “City Room,” Mr. Gelb noted that he one day got his “playful revenge” on reporters.

“The first four I approached claimed they were tied up on assignments I’d given them earlier,” he wrote. “The fifth, Peter Millones, allowed that he was available. ‘Here's a ticket to the World Series,’ I said. It was a box seat in Shea Stadium, the spectacular year [1969] when the Mets won the series.”

Arthur Neal Gelb was born Feb. 3, 1924, in East Harlem and raised in the Bronx. His parents, immigrants from what is now Ukraine, owned a dress shop.

His interest in journalism bloomed after a high school teacher urged him to read the Ben Hecht-Charles MacArthur newspaper comedy “The Front Page,” whose characters made an art of unscrupulous scoop-getting.

Mr. Gelb was unable to serve in the military during World War II because of poor eyesight and, having quit City College of New York in his junior year, became a copy boy at the Times.

In 1946, the year he graduated from New York University, he married Barbara Stone, a fellow newsroom clerk who was the stepdaughter of playwright S.N. Behrman and niece of violinist Jascha Heifetz.

Besides his wife, survivors include two sons, Peter Gelb of Manhattan and Michael Gelb of Upton, Mass; four grandchildren; and a great-granddaughter.

Promoted to drama desk reporter in 1955, Mr. Gelb saw the city’s off-Broadway houses and cabarets — little-chronicled by the paper’s reviewers — as a place where he could make his mark. He asked managers to tip him off to “fresh and daring” talent that could benefit from a Times boost and that displayed “the kind of dissenting voices that had always appealed to me.”

Among them was Bruce, known for his antagonistically off-color humor.

Bruce, pleased with the coverage, invited Mr. Gelb back to the club one night and announced to the audience, “Put the spotlight on that man. That’s Arthur Gelb. He introduced sex to the New York Times.”

Mr. Gelb’s greatest legacy in the theater world was “O’Neill,” a best-selling, 970-page biography written with his wife and published nine years after O’Neill’s death. The Gelbs spent five years writing the book, interviewing more than 400 people.

Jeff Kennedy, president of the Eugene O’Neill Society, said it was the “first major biography of O’Neill,” the only American dramatist to receive the Nobel, and described the work as “impeccably researched.”

The Gelbs later completely revised the volume and wrote other books about O’Neill, including “By Women Possessed,” which is scheduled for publication next year.