Fernande Grudet, best known as Madame Claude, the proprietor of Paris’s most exclusive brothel, shown in 1986. (Laurent Rebours/AP)

For more than a decade, a French business owner known simply as Madame Claude reigned over Paris like an uncrowned queen. She dressed in Chanel, had millions in the bank and was the very model of elegance and discretion.

She seemed to know everything going on in the worlds of politics, commerce, diplomacy, show business and even the criminal demimonde. She enjoyed international acclaim and had the confidence — some would say the protection — of the highest echelons of the French government.

She rose to power as the proprietor of what may have been the most elite and refined brothel in the world.

Madame Claude, whose real name was Fernande Grudet, died Dec. 19 at a hospital in Nice, France, at age 92. He death was first reported by the French media.

Prostitution is not strictly forbidden in France. What is against the law, however, is to procure a prostitute’s services and profit from the transaction. But such niceties seldom bothered Ms. Grudet, who fashioned a comfortable life out of necessity, a dulcet voice and a head for money.

Fernande Grudet, also known as Madame Claude, in 1986. (Michel Gangne/AFP/Getty Images)

Her early years remain sketchy and unsubstantiated. Did she, as she claimed, serve in the French Resistance during World War II? Was she held in a concentration camp? Was she a fallen aristocrat who once sold Bibles door to door, or was she a common streetwalker who went indoors and upscale?

One of the few certainties about Ms. Grudet was a calculation she described in an autobiography first published in the 1970s: “There are two things that people will always pay money for. Food and sex, and I wasn’t any good at cooking.”

It’s unclear precisely when Ms. Grudet remade herself as Madame Claude, but she had set up shop in Paris near an exclusive men’s club no later than 1961. In short order, she developed an international mystique.

Searching for a certain je ne sais quoi among her workforce, Ms. Grudet subjected job seekers to “ferocious” scrutiny, rejecting 19 of every 20 who applied. She quizzed them on history and cultural matters. They had to stand naked before her examining eye and, perhaps even more revealing, show her the contents of their handbags.

They were hired only after passing a closed-door tryout with one of Ms. Grudet’s male friends. Then she groomed the women into what she called “swans,” paying for tutoring, plastic surgery, dental work and expensive couture. She offered pointers on how to improve their bedside manner.

She preferred tall, slender women who spoke several languages and were comfortable “in front of a king, three princes, four ministers and five ambassadors at an official dinner,” she told the Chicago Tribune in 1987. Many of the “Claudettes,” as they were often called, married into nobility, wealth and fame.

As many as 200 call girls worked for Ms. Grudet at a time, reportedly including a countess, the daughter of a top French general, a university professor, fashion models, dancers — and several wives of French public figures. Actress Joan Collins wrote in her 1997 memoir “Second Act” that Ms. Grudet attempted to recruit her during a sojourn in California in the 1970s.

As the sole owner of a legally questionable enterprise, Ms. Grudet handled her customers and staff with — how do they say in France? — a touch of finesse. Most liaisons were arranged by telephone, with Ms. Grudet taking every call.

She collected 30 percent from each encounter but refused to use the terms “prostitute” and “pimp” to describe her business.

“A pimp is someone who forces girls to prostitute themselves, who beats them, terrorizes them and steals what they earn,” she wrote in her autobiography. “With me it was exactly the opposite. I made the bookings and took a commission like the director of a modeling agency.”

The rumors about Madame Claude’s list of clients acquired the aura of myth. There were British bankers, Italian auto tycoons, German industrialists and, according to a 2014 article in Vanity Fair, “half the French Cabinet.”

The CIA allegedly enlisted her services during the 1973 Paris peace talks, aimed at ending the Vietnam War. Ms. Grudet reportedly received carte blanche from French gendarmes because she passed along tips gleaned from pillow talk with underworld figures.

Each Friday, Ms. Grudet dispatched several courtesans on a flight to Tehran, where they were reputedly welcomed in style by the shah of Iran.

Although Ms. Grudet demanded complete silence from her workers, word leaked about other possible customers, including Israeli military leader Moshe Dayan, Libyan strongman Moammar Gaddafi, actor Marlon Brando and painter Marc Chagall, who made drawings of the Claudettes.

On a visit to Paris, John F. Kennedy supposedly requested the company of a woman who looked like his wife, Jacqueline, “but hot.”

The former first lady’s second husband, shipping magnate Aristotle Onassis, was another frequent customer, often accompanied by his lover, opera star Maria Callas.

Movie producer and Hollywood studio chief Robert Evans recalled his first visit to Madame Claude’s in the 1960s, accompanied by French actor Alain Delon.

“ ‘When I stay in his home, I am treated as royalty,’ ” Delon told Ms. Grudet, according to Evans’s 2013 memoir, “The Fat Lady Sang.” “ ‘Now he is visiting me in my home. The only way I can show my appreciation is to treat him the same.’

“She extended her hand. ‘Monsieur, Paris is yours.’ ”

Afterward, Delon said, “I want you to know, Robert, you’ve just met the most powerful and influential woman in all of France.”

Fernande Grudet was born July 6, 1923, in Angers, a provincial city in western France. She said that she was from an aristocratic family, that her father was in politics and that she was educated by nuns.

Other stories suggest that her father ran a small cafe and that young Fernande sold food from a pushcart.

During World War II, Ms. Grudet had a daughter, but the father did not survive the war. The daughter was raised by Ms. Grudet’s mother.

Ms. Grudet later said she was arrested for her work with the French Resistance during the war and spent time in a Nazi concentration camp, where she helped save the life of a niece of French leader Charles de Gaulle.

Some people said they saw a number tattooed on her wrist, which would indicate she was held at the Auschwitz concentration camp and may have been Jewish. But that tale, like so many others, cannot be verified.

Eventually, Ms. Grudet made her way to Paris, where she took “the kind of jobs you take when you have no proper work,” she said in 1987. She was a prostitute for a while, but because she was “never pretty enough,” she decided she was better suited for management.

After years of operating as an open secret, Ms. Grudet saw her empire begin to unravel in the 1970s. A disgruntled prostitute fired a gun at her, striking her in the shoulder and hand, and French authorities charged Ms. Grudet with tax evasion.

She fled to Los Angeles, where she had a marriage of convenience to a gay man to obtain a residency permit. She opened a French bakery that failed, then tried with modest success to reconstruct her Paris business in Hollywood.

Returning to France in 1985, she was arrested on the decade-old tax charges and jailed for several months. Easing into retirement, she occasionally spoke about the life she had known — the flights on private jets with royalty, the A-list parties when all eyes turned to her, leaving movie stars in the shadows.

She began working at a clothing boutique, and it wasn’t long before the Paris police heard that Madame Claude was back in business. Stakeouts and secret recordings — “My dear, those thighs are a little heavy” — led to her arrest in 1992 for “procurement.”

This time, her old friends could offer no help.

“Twenty years ago I was, in effect, employed by the government,” she said at the time. “I had nothing to fear. My clients looked after me, but now they are dead, retired or frightened. Now I have nothing. No friends, no money.”

Ms. Grudet was found guilty. Her prison sentence was reduced to the six months she served while awaiting trial.

There were several books and films about her life, and she released a video in the 1990s about seduction techniques, but the world had changed around her. As people began to understand the darker side of the sex trade, Madame Claude was no longer seen as a simple purveyor of naughty fun.

“She reduced the entire world to rich men wanting sex and poor women wanting money,” Dany Jucard, a Paris Match correspondent, told Vanity Fair.

Ms. Grudet spent her final years in poverty in Nice. Her daughter also lived there, but the two remained distant. When they passed each other on the street, they rarely spoke.

For Ms. Grudet, all was gone: the powerful men, the jet planes, the glamorous women whose lives she shaped, the money. The telephone no longer rang, and in the end she was left only with memories of her charmed life as Madame Claude.

“Everyone enjoyed complete freedom,” she said. “The girls did their job, and I did mine.”

An earlier version of this story incorrectly stated that Aristotle Onassis and Maria Callas were married.