A venerable London art dealer, Patrick Matthiesen was in his second-floor gallery office last year surrounded by stacks of books on the old masters when he opened an email that confirmed his worst fears.

“This will be short,” the March 4 email began. “I lied…”

The sender was an American that Matthiesen knew as A.J. Doyle. Over a correspondence spanning more than two years, Doyle had regaled the dealer with tantalizing tales of life as a former Navy fighter pilot with connections throughout the art world and control over a $2.5 billion family fortune.

Matthiesen, who is 82 years old, grew to trust his new acquaintance sufficiently that he allowed Doyle to broker the sale of a 19th-century Gustave Courbet painting, “Mother and Child on a Hammock,” which the London dealer had been trying to sell for $650,000.

Through Doyle’s maneuvering, the painting was ultimately sold to none other than rock ’n’ roll legend Jon Landau, the longtime producer and manager for Bruce Springsteen who also ranks as one of the country’s top art collectors with a trove including pieces by Donatello, Titian and Tintoretto.

But for months Doyle had stalled in sending Matthiesen his cut of the Courbet sale. In that March email, Doyle was making clear that he had no intention of passing along the proceeds—in fact, he planned to disappear.

“After sending this I will throw my phone in a dumpster, get on the boat and head south until the weather is warm,” he wrote in the message, which was reviewed by The Wall Street Journal.

In his email, Doyle, who is 68 years old, said that he was burdened by depression and alcoholism. And nodding at what he called “past indiscretions,” he hinted that he was not who he claimed to be.

Eight months later, in November, U.S. prosecutors had Doyle arrested and charged him with defrauding Matthiesen. The press release called him “recidivist fraudster.” He is being held in federal jail in Brooklyn and has pleaded not guilty.

The indictment names him as Thomas Doyle, saying that he also used the pseudonyms A.J. and Austin Doyle. Other court records show that Doyle at various times has operated as Thomas O’Brien, Terry Kelly and Dennis Thomas.

Doyle’s court-appointed lawyer didn’t respond to requests for comment.

In a legal showdown that has become the buzz of the international art circuit, Matthiesen has since set out to reclaim his masterpiece, which currently hangs in Landau’s ornate dining room about an hour north of New York City.

Landau paid $125,000—or less than a quarter of what Matthiesen was initially asking—and the dealer alleges in his lawsuit that the sophisticated collector should have known the deal was too good to be true.

Landau says he bought the Courbet fair and square from a reputable New York dealer, whose lawyer says she was legally cleared to resell the work.

Even though neither ever met Doyle in person, both men are the latest additions to Doyle’s own gallery of far-flung victims. It is a collection that stretches from Kansas to Tennessee to New York, with capers that have only grown more brazen over four decades. As they learned, the Courbet affair was hardly the first time this handsome outsider was able to allegedly bamboozle savvy art buyers.

Not even close.

‘Every girl’s dream’
Born in Kansas in 1957, Doyle had logged three theft convictions by his early 20s.

Criminal records unearthed years ago by the Kansas City Star show that he once stole a fur coat and another time impersonated a Secret Service agent. In the early 1990s, the FBI linked him to valuable art inventories known as catalogue raisonnés that had been stolen from Midwestern libraries. Some were later found rebound with their serial numbers removed, making their origins harder to trace.

In 1993, Doyle and his mother, Joann Doyle, were indicted together in Kansas for transporting stolen property across state lines. Doyle eventually confessed to making more than $45,000 from selling stolen books. He was sentenced to 30 months in prison.

FBI agent Ron Elder, now retired, was working the case out of Topeka, Kan., and said he located the Doyles with the help of a jilted girlfriend. Elder recalled that Thomas Doyle was tall, blond and charming.

“Every girl’s dream,” he said.

Jilted girlfriends would become a theme in Doyle’s life. A Kansas schoolteacher who married Doyle told friends she thought he was an investment banker. She later lost $35,000 to him, the Star reported, citing divorce records. Another girlfriend lost a $20,000 art investment to Doyle.

Doyle moved on to scamming working-class people out of jewelry and gold, and once kept $2,500 that he promised a Kansas man he would use to buy a collectible violin. Those victims told the Journal that Doyle came to their homes and spent time with their families, patiently forging bonds, with deep knowledge of jewelry and musical instruments.

He was never pushy, they said, explaining years later how they let their guard down. They never saw their valuables or money again.

In July 2006, Manhattan prosecutors charged Doyle with the theft of a bronze sculpture of a nude dancer by French impressionist Edgar Degas valued at $600,000. Without the owner’s permission, Doyle had secretly sold the sculpture for $225,000 to an antiques dealer. It was then resold via a Manhattan gallery to a buyer in Hong Kong.

The Degas’ whereabouts remained a mystery, but the case suggests that Doyle was learning how to insinuate himself in the blue-chip center of the art world, not merely on its fringes. The sculpture’s owner was Norman J. Alexander, a reclusive former textile executive living in Manhattan.

Alexander, who died in 2011, had amassed valuable art treasures in his five-story townhouse on the Upper East Side.

Doyle met him after claiming to be a descendant of famed art dealer Joseph Duveen, who sold masterpieces to U.S. industrialists in the 1920s and ‘30s. Gary Lerner, a lawyer who represented Alexander, says the collector hosted Doyle at his home many times. They talked for hours about art.

“Mr. Alexander liked his company,” Lerner says. “He was lonely. He struck up what he thought was a friendship with the guy.”

Doyle’s next known caper in 2010 garnered even more attention when he was charged with convincing a private investor to hand over $880,000 for an 80% stake in a $1.1 million deal to purchase a painting by Jean-Baptiste-Camille Corot, “Portrait of a Girl.”

Instead, Doyle secretly negotiated with another buyer to charge $775,000 for full ownership, giving him a $105,000 payday, prosecutors said. Doyle used part of his share to buy a red convertible Ferrari Mondial T Cabriolet.

Police later seized the Ferrari and New York tabloids pounced on the story in part because of a wacky mishap. Doyle had briefly entrusted the Corot to one of his former cellmates, who managed to leave the painting behind in some shrubbery outside an Upper East Side apartment building in New York during a night of heavy drinking.

“Plaster-Piece! Dimwit Loses Million-Dollar Painting After Night on the Town,” the New York Post declared.

A worker in the building later found the painting in the bushes and alerted police.

Jim Wynne, a former FBI agent who worked that case, noticed a pattern emerging in Doyle’s crimes: Consignment fraud. Doyle’s specialty was convincing sellers to let him broker art deals as a middleman, or a runner in art-dealing parlance, only he wasn’t later paying his sellers the full sale price, if anything.

“He’s not running a mill creating fake paintings or running a Ponzi scheme,” Wynne says. “Doyle’s practice is transactional.”

But Wynne figured he’d heard the last of Doyle after attending his 2011 sentencing for stealing that Corot. The New York federal district court judge gave Doyle a tongue-lashing and sentenced him to six years in prison, twice the time stipulated in his plea bargain, citing his record that included 11 convictions.

“Society needs to be protected from you. You are a predator,” the judge told Doyle.

Unlike thieves who carry weapons into museums or use axes to smash-and-grab, art-world scammers rarely get violent—so their prison sentences often get cut short.

“It’s basically a financial crime, and anything under $1 million is usually a probationary matter in terms of prison time,” says Robert Wittman, who formerly served on the FBI’s specialized Art Crime Team. “For the criminal, it’s almost worth it.”

Roughly three years into Doyle’s prison term for the defrauded Corot, he was a free man again.

‘I grew up in the art business’
Matthiesen didn’t appear to be an easy mark. He was born into the cloistered art world as the son of a German Jewish art dealer who fled Berlin in the 1930s and restarted his business in London. Young Matthiesen grew up surrounded by his father’s illustrious inventory and went on to study art conservation and joined a major gallery, Colnaghi, before opening his own in 1978.

Today, his eponymous gallery sits in a London neighborhood dotted with rare-book stores, high-end tailors and auction houses like Sotheby’s and Christie’s.

Doyle did his homework.

“My name is Austin Doyle. Like you I grew up in the art business,” he wrote Matthiesen in an introductory email in mid-December 2022. He said he bought and sold art “on the side.”

“I am presently in Ukraine as a consultant to the US Government,” Doyle added, explaining why he might be challenging to reach by phone.

Matthiesen responded warmly. “How exciting being in Ukraine,” he wrote back. “I am a great supporter.”

Over the next two years, Doyle sent Matthiesen a stream of emails and text messages. Doyle referred to his past as an F18 fighter pilot in the Navy. When he wasn’t in Ukraine, he might be in Africa with spotty cellphone service.

Doyle portrayed himself as a man at ease with money and the rarefied world of high-end art.

“I manage my family’s trust,” he wrote to Matthiesen. “We buy and sell art. I have about 15 useless cousins that try every year to dissolves[sic] the trust. That way they can get their share of approximately $2.5b.”

Matthiesen says he had some reason to see sincerity in Doyle’s motives, particularly after Doyle sent his gallery a drawing in 2023 whose owner said he believed it was by Michelangelo.

Matthiesen suspected that Michelangelo’s assistant, Daniele da Volterra, likely drew the picture instead, and consulted experts who agreed. The drawing still impressed the veteran dealer, though. Even a work by the famed Michelangelo aide was a valuable find.

“To me this was the clincher,” Matthiesen later said in an interview. “Because here was a man who clearly, once again, had access to real works of art.”

The owner of the drawing, a New York dealer, later told the Journal that he had traveled with the drawing to London to be seen by a renowned British expert and a potential Russian buyer. Through a series of deceptions, an associate of Doyle’s diverted it to Matthiesen instead without the intended expert finding out.

Matthiesen didn’t buy the drawing, but the pump was primed. Matthiesen would grow comfortable enough to let Doyle in on a potential deal of his own—the Courbet, which he had bought in France for roughly $112,000 in August 2015.

Matthiesen then had it restored and authenticated, an upgrade that would typically ratchet its value. In 2017 and again in 2023, he sent it to the world’s pre-eminent old masters fair, the European Fine Art Fair in Maastricht, the latter with a price equivalent to $701,500.

During the 2023 fair, Landau was among the collectors who stopped to eye the work but didn’t make an offer. He later viewed it again when it was on display at a New York gallery, and again passed.

By July 2024, the work remained unsold, a scenario that can further dampen a work’s appeal because collectors tend to pounce more readily on fresh finds in the marketplace compared to works they deem to be shopped around.

For months, Doyle tried to sell various works to Matthiesen, to no avail. Matthiesen says he typically would have done a deep dive on his background before buying anything from an email acquaintance.

But he was intrigued when Doyle casually proposed helping Matthiesen lock in a buyer for the Courbet. Matthiesen asked around about A.J. Doyle and didn’t hear anything worrisome.

Soon after, Doyle told Matthiesen he found a person named Chris willing to buy the Courbet painting for $550,000. All that “Chris” needed to do was complete a big real-estate deal and then he would send the money.

As the months ticked by, the supposed real-estate deal bogged down and Matthiesen stopped hearing from Doyle. Instead, Doyle’s updates started arriving from someone claiming to be his assistant, who went by Michelle.

She offered excuses that increasingly grated on Matthiesen. At one point, she told him that Doyle was out of touch while on assignment in Africa.

Then in the fall of 2024, a colleague of Matthiesen heard through a contact at Sotheby’s in New York that Landau was showing his new Courbet to friends as the latest addition to his collection.

Incredulous, Matthiesen emailed Doyle, who wrote back that yes, in fact, Landau and “Chris” had bought the painting together. Doyle promised to send the money as soon as possible.

He didn’t tell Matthiesen that Landau had only paid $125,000 for the work before fees and framing, or around $147,000 all in.

Doyle also never sent Matthiesen a dime.

‘I’m shocked’
Landau, who began visiting European museums and collecting art while on Springsteen’s epic tours in the 1980s and 1990s, never teamed up with a “Chris.” Instead, he says he got a call about a Courbet from a New York dealer, Jill Newhouse, who had sold him several paintings over the years.

Newhouse had been told by an associate of Doyle that it came from an undisclosed collector in Connecticut.

She emailed an image to Landau, who called her back immediately.

“I’ve been offered this painting over the past decade, and I have no interest,’” Landau told her.

Newhouse suggested he make an offer. He smelled a potentially good deal.

“A buck and a quarter,” Landau told her, meaning he’d be willing to pay $125,000. He expected some negotiation, but Newhouse called him back and told him that the sellers had accepted.

“I’m shocked,” Landau told her.

Roughly the size of a magazine cover, “Hammock” is only one of 18 Courbet works that Landau has bought over the years, and it’s hardly the most expensive or significant example. Still, he said the work depicting a young woman relaxing with an infant nestled on her lap provides him “a little jolt” each time he looks at it.

Landau’s lawyer says the collector didn’t know the dealers involved included Doyle and his associate, Shalva Sarukhanishvili, who had also helped arrange the showing of the supposed Michelangelo drawing in London in 2023.

Newhouse’s lawyer Amelia Brankov says the dealer ran checks to make sure the work wasn’t reported stolen and says any grievance Matthiesen has should be with Doyle.

Sarukhanishvili’s lawyer also says his client was deceived by Doyle. He said Sarukhanishvili is an art dealer who has worked with Doyle in the past and “has always understood their dealings to be legitimate.”

According to Matthiesen and his lawyer, Steven Schindler, the shock over the price tag is exactly why Newhouse and Landau both should have suspected something was fishy and done more to check its phony back story.

Landau’s lawyer, Jonathan Kraut, said “Matthiesen’s suggestion that Mr. Landau failed to exercise due diligence in buying a painting from a well-known and respected art dealer is absurd.” He added that the onus fell to Matthiesen to check out Doyle’s credentials and said Landau paid a fair price for it amid a market downturn.

Jane Levine, an art lawyer and managing partner at the New York-based ArtRisk Group, says the case may ultimately hinge on what kind of consignment contract or agreement Matthiesen signed with Doyle to act as his agent.

Matthiesen, in his lawsuit, says Doyle got him to issue an invoice for $550,000 based on lies.

Wittman, the former FBI agent, says he expects art-world insiders to remain riveted to this case as it winds through the courts because both Matthiesen and Landau appear to have reasonable claims to the Courbet.

“We all want a good deal,” Wittman says. “That’s why people buy fake paintings or buy them on the cheap…It’s the hunt for treasure.”

As for Doyle, the multibillion-dollar family fortune doesn’t exist, prosecutors say. The U.S. Navy and other military record-keepers have no record of Doyle having served.

During the time Doyle’s supposed assistant “Michelle” was emailing Matthiesen that Doyle couldn’t be reached on his far-flung travels, Doyle never left the U.S., the government says.

On that fateful day in March when he sent Matthiesen that confessional email, Doyle strongly suggested that his disappearing act would be final. He planned to “turn on the Moody Blues, open a bottle of bourbon and eat my 1911 acp for dessert,” he wrote, referring to a semiautomatic pistol long used by the U.S. military.

In truth, he was arrested in Connecticut, where he had been living for weeks out of his car in a hotel parking lot.

Write to Jenny Strasburg at jenny.strasburg@wsj.com and Kelly Crow at kelly.crow@wsj.com