Robert Osborne, the urbane, silver-haired film historian who had been the principal host of the Turner Classic Movies cable channel since its founding in 1994 and was a genial ambassador for an otherwise vanished era in filmmaking, died March 6 at his home in New York. He was 84.

A friend, theater director and producer David Staller, confirmed the death but did not disclose the cause.

Former Washington Post TV critic Tom Shales once praised TCM — where stars such as Clark Gable, Fred Astaire and Rita Hayworth still reign as celluloid kings and queens — as “the most reliable source of pure enchantment in the cable universe.”

TCM, available in more than 85 million homes, has drawn an intensely loyal following in an era of seeming indifference to the fate of movies and stars from yesteryear. Film revival theaters have all but disappeared. And TCM’s onetime cable rival, American Movie Classics, has ceased trying to live up to its name, instead venturing into programming territory from Will Smith action movies to series such as “Mad Men.”

Besides its magnificent film trove, TCM owed a sizable portion of its growth as a brand to Mr. Osborne, an unalloyed cinephile and former acting protege of Lucille Ball’s who once was actress Bette Davis’s date to the Academy Awards.

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He wrote official histories of the Oscars and was a longtime columnist for the Hollywood Reporter, a show-business trade publication, but his gift was never about going for the journalistic jugular. “I would be told secrets, and I would keep the secrets,” he once said, adding that he learned actor Rock Hudson had AIDS long before it was publicly known.

Mr. Osborne was endowed with a talent for befriending stars, many of them marquee movie names of his youth. They were relegated to the shadows by the time he got to know them in the 1960s, forgotten by an industry that had unsentimentally moved on. “Somebody like Dorothy Lamour,” he told the New York Times, “she adored me. I knew she had sold more war bonds during the Second World War than almost anybody in Hollywood.”

His ingratiating personality and insider knowledge led to work as a host on The Movie Channel from 1986 to 1993. American Movie Classics tried to recruit him as a daytime host, but he accepted an offer from the upstart TCM because it featured more of the fare he treasured — from Marx Brothers comedies of the 1930s to later works by directors such as Akira Kurosawa and Mel Brooks. And it was a chance to work in prime time.

As the suave, soothing public face of TCM, Mr. Osborne delivered revelatory tidbits before and after each screening, and he gently coaxed stars well past their prime (Patricia Neal, Tony Curtis, Betty Hutton) to speak tantalizingly of their career highs and lows.

Erudite without being snobbish, Mr. Osborne conveyed a seemingly limitless ardor for the job. He could enthuse about the 1940 Ann Sothern vehicle “Congo Maisie” as much as the Oscar-winning epic “Gone With the Wind” (1939).

The TCM host worked hard to intrigue first-time viewers, garnishing his segments with stories about backstage affairs and egos run amok amid filmmaking, and he tried to find new approaches to entice more-experienced viewers such as himself.

“I thought when asked for my ninth introduction to ‘The Philadelphia Story’ that I might pass,” he told the Toronto Star, referring to the frequently shown 1940 comedy starring Cary Grant, Katharine Hepburn and James Stewart. “But I did it as a salute to Ruth Hussey, the neglected fourth wheel, Oscar-nominated for her performance.”

Richard Schickel, a filmmaker and Time magazine movie critic, once praised Mr. Osborne: “You feel like it’s not just a guy up there reading copy that people prepared for him to read. That’s a good quality and increasingly rare in the television climate of our times. He’s something a lot more than just a talking head.”

Robert Jolin Osborne was born on May 3, 1932, in Colfax, Wash., a farming community. The local bijou provided an escape from his less-than-glamorous surroundings.

“The people I knew were all talking about crops,” he once told the Newark Star-Ledger. “But in the movies, all the women were Manhattan heiresses, and Cary Grant was always in evening clothes.”

He was bewitched not just by movies, but also by the boldly illustrated movie posters and fan magazines that featured impossibly alluring actresses such as Lana Turner and sloe-eyed Ann Sheridan. His fascination with movie promotion led him to study advertising and then journalism at the University of Washington.

He took acting roles in Seattle and his dashing good looks — he resembled actor Robert Wagner — led to a contract with a television production company run by Ball, the TV comedienne, and her husband, Desi Arnaz. Mr. Osborne became a regular part of Ball’s entourage, and she was greatly impressed with his knowledge of 1930s character actors such as Edward Everett Horton and Donald Meek.

Mr. Osborne’s social life, although not his acting career, was bubbling. His biggest role was a brief appearance in the 1962 pilot episode of “The Beverly Hillbillies.” Ball told him he lacked the survival skills for the cutthroat profession. “We have enough actors,” he recalled her saying. “We don’t have enough writers.”

Because of his interest in filmmaking of the past, he published an official history of the Academy Awards in 1965. He updated the book every few years and joined the Hollywood Reporter in 1977, eventually settling in at its New York office.

He became the publication’s “Rambling Reporter” columnist, covering film, theater and TV. He also moonlighted as an entertainment correspondent for various TV shows, including the CBS “Morning Program,” before the TCM job.

TCM began with a modest viewership, but its reputation grew rapidly under Mr. Osborne. The network now hosts an annual, frequently sold-out movie festival in Hollywood, as well as a yearly cruise that draws thousands of passengers and has featured guest stars such as Eva Marie Saint and Shirley Jones.

Over the years, TCM added other hosts, including Ben Mankiewicz, a scion of Hollywood royalty, and brought in actors such as Alec Baldwin, Drew Barrymore and Rose McGowan to appear with Mr. Osborne and add contemporary cachet.

But Mr. Osborne remained the network’s clear star, a matinee idol in his own right when he sat down to interview celebrities.

“You look into those beautiful blue eyes and you know that nothing can go wrong,” Saint, an Oscar-winner who starred in “On the Waterfront” and “North by Northwest,” told the New York Times in 2014. “He’s one of us, but he also knows a lot more than any of us.”

Mr. Osborne said he often was stopped on the street or at parties by people who tried to stump him with movie questions. At one soiree, he told the Times, he was cornered by a know-it-all.

“Oh, I’ll bet I know a movie you’ve never heard of,” the person said, “ ‘Where the Sidewalk Ends.’ ”

“Well,” Mr. Osborne responded. “Do you want me to tell you who’s in it in order of their billing or would you rather I tell you what theater it played in New York and for how long?”

He explained to the Times, “I just have that kind of mind. But if someone asks me what time it is on the clock in ‘Gone With the Wind’ when Rhett Butler carries Scarlett up the stairs, sorry, I don’t know.”

CORRECTION: The obituary initially described David Staller as his life partner, based on Mr. Staller’s description at the time. They were longtime friends. The obituary has been revised.