The media baron Si Newhouse, chairman emeritus of Condé Nast, publisher of Vogue, Vanity Fair, the New Yorker and other leading magazines, has died. He was 89 and had suffered from a long illness.

In a statement on Vogue.com, editor-in-chief Anna Wintour said: “Si Newhouse was the most extraordinary leader. Wherever he led, I followed, unquestioningly, simply because he put as much faith in me as I had in him.

“Si never looked at data or statistics, but went with his instincts and expected his editors to do the same. He urged us to take risks and was effusive in his praise when they paid off.

“This humble, thoughtful, highly idiosyncratic man, quite possibly the least judgmental person I’ve ever known, preferred family, friends, art, movies, and his beloved pugs over the flashiness of the New York media world.”

Announcing Newhouse’s death to staff, Condé Nast’s chief executive, Bob Sauerberg, wrote: “In all realms, he wanted Condé Nast and its writers, artists and editors to be at the center of the cultural conversation.”

Nephew Steven Newhouse, chair of Condé Nast owner Advance Publications, told the Associated Press: “He was passionate about journalism and he supported journalists and editors. He set an example of caring about the right things in media, which is great stories, great design, great magazines, great websites.”

Newhouse became chairman of Condé Nast in 1975, going on to revive the fortunes of Vanity Fair and to purchase the New Yorker – to the consternation of many long-serving staff members and readers – in 1985. In an interview with the New York Times in 1989, he said some of the secret of his success lay in the fact that he was “not an editor”.

“I flounder when people ask me, ‘What would you do?’” he said. “We feel almost that whichever way it goes, as long as it doesn’t do something absolutely screwy, you can build a magazine around the direction an editor takes.”

Though his Condé Nast stable included magazines that did much to shape American fashion, literature and design, Newhouse himself was known for his lack of personal style.

“Si Newhouse is nothing like his magazines,” read an Observer profile of Newhouse in 2009. “Short, physically unimposing, dressed for the office in khakis and beat-up loafers, he’s the opposite of glamorous. ‘He’s always had the luxury of being himself,’ says a friend. He’s notably inarticulate, speaking softly, with long, excruciating pauses between words.

“A decision to commit millions of dollars might be communicated with a ‘very, very quiet whispered yes’, says one former editor.”

In the same profile, the editor of the New Yorker, David Remnick, said: “He loves magazines, meaning the whole and all of it, the variety of things published, the business details, the visions and actions and personalities of his editors, the problems, the problem-solving, the ink and paper … the all of it.”

Si Newhouse and Elizabeth Hughes, VP publisher of the New Yorker, at a 2007 Condé Nast party in New York. Photograph: Patrick McMullan/Patrick McMullan via Getty Images

Samuel Irving Newhouse Jr was born on 7 November 1927 in Staten Island, the grandson of Russian Jewish immigrants. His father, Sam Newhouse, bought the Staten Island Advance in 1922 and used its profits to buy more papers.

Newhouse attended the elite Horace Mann high school in the Bronx. Among his classmates was Roy Cohn, a lifelong friend who went on to become a New York powerbroker, aide to the infamous Wisconsin senator Joseph McCarthy and mentor to the young Donald Trump.

Newhouse dropped out of Syracuse University in his junior year, worked at his father’s newspapers and lived a playboy lifestyle. By the mid-60s he had found a place at Condé Nast. Once on the board of the Museum of Modern Art, he had a major collection including works by Picasso, Andy Warhol and Jasper Johns.

Newhouse also owned, with his younger brother Donald, Advance Publications, a media empire which includes 26 newspapers based in cities across the US, including the Newark Star-Ledger in New Jersey, the Plain Dealer in Cleveland, Ohio and the Oregonian, based in Portland. Advance also has a 25% stake in Discovery Communications and cable TV assets.

In 1998 he sold Random House for around $1.1bn. While he owned the publishing house, he commissioned a book by Donald Trump. The Art of the Deal became an infamous bestseller.