Outside the rarefied world of art dealers and collectors, where discretion is often prized nearly as much as the art itself, the Nahmad family does not attract the same recognition as some of their fellow billionaires.
But for those who trade in multimillion-dollar paintings, they have long been a major presence at the premier auctions held every spring and fall at Sotheby's and Christie's, where they often descend, wives and children included, and have been known to argue loudly with one another, even while others around them engaged in more genteel bidding.
Despite sneers from some of their more staid peers who have accused them of unfairly negotiating special terms with auction houses, they are among the most powerful, wealthy and colorful members of the elite global club of fine art dealers.
"They have sold more works of art than anybody alive," Christopher Burge, the former chairman of Christie's New York, once said.
But on Tuesday, the family's New York flagship gallery, the Helly Nahmad Gallery, at the opulent Carlyle Hotel in Manhattan, was filled with agents from the Federal Bureau of Investigation conducting a raid. An indictment unsealed on Tuesday charged its owner, Hillel Nahmad, 34, with playing a leading role in a far-flung gambling and money-laundering operation that stretched from Kiev and Moscow to Los Angeles and New York.
The case features a wide cast of characters, including a man described as a Russian gangster accused of trying to rig Winter Olympic skating competitions in Salt Lake City and a woman who once organized high-stakes poker games for some of Hollywood's most famous faces.
In all, 34 people were charged on Tuesday with playing a part in what federal prosecutors described as two separate but interconnected criminal groups — one operating overseas and the other in the United States. Together, they are accused of laundering more than $100 million in gambling money.
In addition to charges that Mr. Nahmad helped finance a multimillion-dollar gambling ring in the United States, the art dealer is accused of defrauding an unnamed person by selling him a painting for $300,000 when it was worth only $50,000, according to the indictment.
Mr. Nahmad, the indictment said, also wired money — once for $500,000 and another time for $850,000 — from his father's bank account in Switzerland to a bank account in America to help finance the gambling operation.
The Nahmad family's rise to prominence dates from its roots in Aleppo, Syria, where the family's patriarch, also named Hillel, was a successful banker in the middle of the last century.
He had three sons, David, Ezra and Giuseppe; Giuseppe died last year in London.
David Nahmad, whose son Hillel ran the New York gallery, has been described as a risk-taker in both business and life. In Monte Carlo, he won the World Championship of Backgammon in 1996.
Over the years the family has amassed an estimated 300 Picassos worth $900 million, and about 4,500 other works by artists including Monet and Miró, many secreted in a duty-free warehouse near the Geneva airport. It is a treasure that Forbes estimated to be worth over $3 billion. Before this week, Hillel Nahmad's gallery was a cynosure of refinement and wealth, with masters like Wassily Kandinsky and Francis Bacon on the walls.
With an entrance at Madison Avenue and 76th Street, the gallery's connection with the Carlyle, itself synonymous with privilege, added to its prestige. The gallery has been at the Carlyle since at least the late 1990s.
However, even before the F.B.I. raid at 7:30 a.m. on Tuesday, the gallery's windows were covered with brown paper, which is unusual since the spring art season is just kicking into high gear.
A sign on the door said, "We are closed for renovation, please ring the bell or call."
A man who answered the phone at that number declined to speak to a reporter.
According to the indictment, Hillel Nahmad was one of the leaders of a "high-stakes illegal gambling business run out of New York City and Los Angeles that catered primarily to multimillionaire and billionaire clients."
He was expected to surrender to the authorities in Los Angeles on Tuesday. His lawyer could not be immediately reached for comment.
The indictment also named Molly Bloom, who made headlines in 2011 for her role in arranging clandestine games for high-rollers, including Tobey Maguire, Leonardo DiCaprio, Matt Damon and Ben Affleck.
Federal law enforcement officials would not say whether the poker games Ms. Bloom ran in Los Angeles in 2011 came under scrutiny during the course of the investigation. But the charges in the indictment relate to her conduct between 2010 and the present. The indictment did not name any of the high-profile players who investigators said were involved in the poker games held in New York and Los Angeles.
According to the indictment, the organization would enforce payment of gambling debts through coercion. One client surrendered a 50 percent interest in his business, Titan P&H plumbing company in the Bronx, to repay a $2 million gambling debt. Some of the money generated by the scheme was also used to buy expensive property, including an apartment at Trump Tower on Fifth Avenue.
One of the defendants, Vadim Trincher, helped run the scheme from the $5 million apartment, according to prosecutors, who said that $75,000 in cash and $2 million in chips from the Bellagio casino in Las Vegas were seized from the apartment.
At the center of the overseas operation detailed in the indictment was Alimzhan Tokhtakhounov, 64, whom prosecutors describe as the leader of a Russian organized-crime gang.
Mr. Tokhtakhounov, according to the indictment, was a "Vory V Zakone," sometimes known as a Vor or a "thief in law," the highest level of Russian gangsters.
Between December 2011 and January 2012, Mr. Tokhtakhounov was paid $10 million for his leadership role in the organization, according to the indictment.
Mr. Tokhtakhounov, the indictment said, oversaw the laundering of money generated by a huge sports-betting operation in the former Soviet Union that served Russian oligarchs.
Mr. Tokhtakhounov, who remains at large, was indicted in 2002 on charges that he was part of a scheme to rig the results of the Winter Olympic finals in Salt Lake City in pairs figure skating and ice dancing.
In July 2002, Italian tax authorities detained Mr. Tokhtakhounov at his villa in Tuscany at the request of federal prosecutors in New York.
According to a criminal complaint filed in federal court in Manhattan in that case, he was accused of working with an unidentified member of a Russian crime gang and an unidentified Russian skating official to rig the competition. He helped secure a gold medal for Russia in the pairs event in exchange for a victory for the French ice dancing team, according to the complaint.
However, Italy's highest court overturned an extradition order, and he was never brought to the United States to stand trial.
In 2008, Mr. Tokhtakhounov, who has been linked with powerful Russian politicians, including some close to President Vladimir V. Putin, was interviewed by ESPN and denied all the charges against him regarding the Olympics scandal.
"All that's being written about me is completely untrue," he said. Still, he seemed to revel in his lavish lifestyle.
"I am not a poor man," he said. "I am a wealthy man. I work a lot. I work hard."