Gelb joined the ranks of the Times in 1944 as a copy boy. Over the next 45 years, he held the positions of reporter, editor and executive, retiring in 1989 as managing editor. He wrote of many of his experiences at the paper in the 2003 bestselling memoir "City Room."

He arguably made his greatest impact at the Times as a member of the theatre department in the 1950s. As a junior culture writer and theatre critic, he was among the first New York reporters to write extensively (and enthusiastically) about the Off-Broadway scene. Among the artists he discovered early on in their careers were Barbra Streisand, Woody Allen and Lenny Bruce.

Among the most memorable incident of these early years — and one that arguably changed the course of Off-Broadway history — came one summer day when Mr. Gelb found himself in charge of the theatre department. Lead drama critic Brooks Atkinson was on vacation and the second-in-commend was absent as well when a stubborn and desperate young impresario named Joe Papp visited the Times offices. Papp, ferried to the building on W. 43rd Street by the seasoned press agent Merle Debuskey, wanted Atkinson to come downtown that night and review a free outdoor Shakespeare production he was presenting at the East River Amphitheatre. Papp feared his fledgling enterprise would go under soon without the attention and money a Times review could bring. When Gelb replied it was impossible, that he was too busy, Papp parked himself in a chair and refused to move until the critic changed his mind. Gelb acquiesced.

Gelb only attended half of The Taming of the Shrew before the show was rained out, but he wrote up a positive account of the event. When Atkinson returned, he quizzed Gelb about Papp and the production. At the younger man's urging, Atkinson attended the show himself, and Papp's future was assured. In the decades to come, Papp and Debuskey would often turn to Gelb when they had a cause or a production to advocate.

In 1962, Gelb and his wife Barbara published "O'Neill," a biography of playwright Eugene O'Neill, whose works had always been a favorite of the reporter's. Published just nine years after the playwright's death, and five years after the first staging of Long Day's Journey Into Night, the book helped to revive O'Neill's critical reputation. For many years, it was regarding by many as the definitive biography of the dramatist. The couple, however, continued their research and, in 2000, came out with "O'Neil: Life With Monte Cristo," a sort of revision of the earlier work which took advantage of new information and materials not originally available to the Gelbs. A third volume about O'Neill, "By Women Possessed," will be published in 2015. In 2006, Gelb was a writer and commentator in an "American Experience" episode on PBS that focused on O'Neill.

Arthur Neal Gelb was born on Feb. 3, 1924, in East Harlem. His parents, Daniel and Fanny, were Jewish immigrants from Czechoslovakia who made and sold children's dresses out of a small shop. He attended City College, but dropped out and soon after was hired by the Times as a copy boy. There he met his future wife, Barbara Stone, who was also employed by the Times. Of less humble origins, Stone was the niece of the violinist Jascha Heifetz and the stepdaughter of playwright S. N. Behrman.

Gelb is survived by his wife, his son Peter Gelb, who is director of the Metropolitan Opera, and another son, Michael.