Peter W. Kaplan, who in his 15 years as editor was credited with making The New York Observer both pertinent and impertinent as it gleefully chronicled the every move and shake of the city’s movers and shakers, died on Friday in Manhattan. He was 59.

The cause was cancer, his brother James said.

Founded in 1987 by the investment banker Arthur L. Carter, The Observer, in the words of its website, observer.com, seeks to report on “finance, media, real estate, politics, society, tech and culture with an insider’s perspective, a keen sense of curiosity and a sharp wit.” Published weekly on pinkish paper that in its smoked-salmon hue trumpets Gotham, it reaches a primarily high-income readership.

Though its circulation has long been small — about 50,000 in Mr. Kaplan’s day and only slightly higher now — the newspaper became, under his stewardship, required reading for the very demographic it skewered.

Appointed in 1994, Mr. Kaplan served the longest term of any Observer editor. During his tenure, the paper featured the work of journalists renowned for a cutting-edge sensibility, among them Joe Conason, now the editor in chief of the political website The National Memo; Nikki Finke, who went on to found the entertainment-industry site now known as Deadline.com; and Choire Sicha, who later helped found The Awl, the current-events site.