For more than a century, Huguette Clark lived in a world of unlimited wealth and, by her own choice, impenetrable silence. When she died May 24 at age 104, the copper heiress had been a recluse for more than 75 years, rarely seen even by the people who worked for her. The cause of her death, at a New York City hospital, was not disclosed.

She was the daughter of William A. Clark, a U.S. senator and Gilded Age copper magnate from Montana, who was reputed to be one of the two richest industrialists in the United States, rivaled only by John D. Rockefeller.

The known facts of Mrs. Clark’s life are few but tantalizing. She rarely saw Montana and spent much of her early life in Paris and New York; she spoke English with a French accent; and, in her teens, she took dancing lessons from Isadora Duncan. During the flapper era of the 1920s, she was a society-page fixture as one of the country’s most eligible young women.

Two years after she was married in 1928, Mrs. Clark went to Reno, Nev., to obtain a divorce. The last photograph taken of her was made the day her divorce became final. She reclaimed her maiden name and preferred to be addressed as “Mrs. Clark” thereafter. She never married again and had no children.

Instead, she retreated into a world of opulent isolation and enduring mystery. She lived in the largest apartment on New York’s Fifth Avenue, which she shared for decades with her mother and a prized collection of French dolls. She owned multimillion-dollar estates in Connecticut and California that she hadn’t seen in decades. She liked to watch cartoons on television.

For reasons unknown, Mrs. Clark spent the final 23 years of her life sequestered in New York hospitals, despite being in relatively good health. She was shielded from the public eye by a series of assumed names and by a small group of loyal retainers who would come under legal scrutiny.

At the time she died, she was worth an estimated $500 million. She gave money to museums and other charities but was not known as a major philanthropist or for endowing any widely known foundations.

Anyone who wanted to see her, including distant relatives, was turned away. Even her longtime lawyer said he knew her only as a shadow and a voice from behind a closed door.

Late in 2009, Mrs. Clark’s bizarre life became an Internet sensation when investigative reporter Bill Dedman of learned that her tree-shrouded estate in New Canaan, Conn., was for sale at $24 million.

Dedman discovered that Mrs. Clark had never spent a night at the country retreat, which she had bought in 1952. She last visited her seaside mansion in Santa Barbara, Calif., in the 1950s.

One of Mrs. Clark’s cousins told Dedman, “She was just a quirky person who couldn’t contend with the outside world.”

Huguette Marcelle Clark was born in Paris on June 9, 1906. Her father, then 67, was a sitting U.S. senator, one of Montana’s three “copper kings” and the very definition of a rapacious, self-made mogul.

William Andrews Clark was born in a log cabin in Pennsylvania in 1839 and moved west in his teens. He amassed a fortune by purchasing defaulted loans in Montana’s copper mining country and by starting related businesses.

He eventually owned railroads, banks, gold mines, electric companies, cattle, timber interests, newspapers and a Mexican coffee plantation. He was a principal founder of Las Vegas, which was established as a maintenance stop for one of his railroads. The county surrounding Las Vegas is named for Clark.

In 1898, Clark tried to finagle his way into the Senate, but his bribery of the Montana legislature was so blatant that the Senate refused to seat him. The result was the 17th Amendment to Constitution, requiring the direct election of senators by popular vote.

“I never bought a man who wasn’t for sale,” Clark said in response.

The people of Montana elected him to the Senate in 1900, but he scandalized polite society when he announced that he had been secretly married in 1901 to his much-younger second wife, Huguette’s mother.

Clark retired from the Senate after a single term and settled in a 121-room mansion he built on New York’s Fifth Avenue, where his daughter grew up surrounded by priceless artwork and ornate tapestries and sculptures.

When Clark died at 86 in 1925, a Washington Post obituary described him as “the greatest individual mine owner in the world and probably among the dozen wealthiest men.”

His fortune was estimated at about $300 million, or more than $3 billion in modern currency.

His daughter inherited a fifth of his estate, including his art collection, which she helped distribute. Paintings by Titian, Van Dyck, Rubens and Corot became part of the permanent collection of Washington’s Corcoran Gallery of Art, where they are housed in the Walker wing.

Mrs. Clark was reportedly devastated by the death of her older sister from meningitis in 1919. Not long after her brief marriage in the 1920s to William Gower, one of her father’s employees, she was linked with an impoverished Irish duke. She commented that great wealth could be an impediment to happiness, then closed the doors to the public forever.

Only a few scattered reports about her later life leaked out in the ensuing decades. Her mother once owned a set of four Stradivarius instruments — two violins, a viola and a cello — that had belonged by the great Italian violin virtuoso Niccolo Paganini. The instruments were donated to the Corcoran and, in 1994, sold to a Japanese foundation for $15 million.

For Mrs. Clark’s 50th birthday, her mother gave a Stradivarius violin called “the Virgin.” Known for the perfection of its tone, it was sold for $6 million in 2001.

Last year, at the behest of Mrs. Clark’s distant relatives, Manhattan’s district attorney began investigating her lawyer and accountant for possible mismanagement of her financial affairs. No charges have been filed.

Mrs. Clark’s 42-room apartment overlooking Central Park is worth an estimated $100 million. She had not been seen there since 1988.