Cohen adored his mother, moving her from France to foggy San Francisco first, thento La Jolla, then Hawaii, but she gave up very, very little about his past. He let it beknown that she was a pied noir, a French North African, and that his seldom-mentioned father was a cabdriver in provincial France. Cohen said he never went to college but that as a teenager he had been a national whiz at selling encyclopedias door-to-door.

Soon Cohen graduated from prints to paintings. "He came by my gallery in the early eighties," says Martin Muller. "He bought a painting. That's the way you seduce a dealer -- you buy work." In 1988, he took over a fourth-floor space on Sutter Street, an area thick with galleries. He was living pretty well, sailing a big sloop in the bay and doing tae kwon do, but he was tiring of San Francisco's limited horizons and at the end of the eighties moved to Malibu.

It was in L.A. that Marc Richards, himself a dealer, first met Cohen. "He quickly took to the resale market, which was booming, and played it as well as anybody I know," Richards says. Essentially, Cohen was churning paintings the way he had churned prints. "He would flip things for 5 percent," says a Los Angeles dealer. "He would have high volume, low overhead, and low profits. But a lot of business." Manny Silverman, another L.A. dealer, was struck by his pace. "He bought a Joan Mitchell and drove it from La Jolla," Silverman says, selling the piece within 24 hours.

"He was a risk-taker. He would go out on a limb and buy a million-five painting," a dealer says. "He treated art as a commodity. He knew in his mind everything that had sold, when it had sold, and the price; it was almost like baseball cards."

In 1993, Cohen met Tanya Bonakdar, a slender, fine-boned Briton with a consuming interest in the newest art. Cohen fell in love and moved to New York with her.

He opened a gallery at 1018 Madison. Tanya broke off their affair after a couple of years, but he funded a new gallery for her, closed his own, and returned to his forte, selling paintings dealer-to-dealer. Then he caught a glimpse of every runner's dream: the truly big deal.

Marc Chagall died in1985, leaving a huge archive of late work to his known heirs. Then another claimant popped up: David McNeil, an illegitimate son by a model, who secured 10 percent of the hoard. McNeil had been financially supported for some years by Jean-François Gobbi, who got to manage McNeil's birthright as a quid pro quo. Gobbi reputedly had an apartment in Venice on the Grand Canal and a mighty yacht to go along with his reputation as a tough operator. In 1995, the Chagall estate offered another slice of the archive for sale. The heirs approached Sotheby's. The works "were all from the last fifteen or twenty years ofhis life," says David Nash, who put together Sotheby's proposal. "But Mr. Gobbi came back for a second helping. He exceeded our offer by far." His bid is said to have been $65 million.

That same year, Cohen met Gobbi in Miami. "He was always on Mr. Gobbi's yacht, and he was very impressed by Gobbi," Muller says. In 1997, Gobbi offered Cohen a bite at the Chagalls. So he contacted the Mullers for backing. "We were first approached for a hundred-million-dollar package deal," Martin Muller says. "We were thinking to put together a pool with some of our friends. First a deal for fifteen to twenty million, then the idea to do this in several installments, because who needs to put 800 Chagalls on the market at once? Of course, Michel wanted to do only the whole thing." Swiss caution prevailed. Cohen swiftly found another backer, a Los Angeles real-estate investor. They bought only 80 Chagalls, but Cohen was now a player, too.

Cohen, while keeping up his gallery on Madison, returned to Malibu that year and married Ulrike, a German dealer. "She had been in Colombia. She had dealt Boteros. And she had bought a Diego Rivera for some heavy hitter in the Caribbean," recalls Louis Stern, another dealer.

Cohen bought a white house overlooking Point Dune, the northeasterly tip of Santa Monica Bay. "He wanted the best things in life," says Marc Richards. "He would buy Mercedes after Mercedes. He would change them every three months. We would laugh. But nobody saw any harm in it."

Life in Malibu was grand. Cohen bought the adjoining plot of land, and Ulrike followed rich-woman pursuits, riding horses and taking yoga classes. They doted upon their children, Chloe and Noah. "She said she has one damn nanny after the other," says an Austrian visitor, Eva Bockl. "She was recommended this nanny at her yoga club who had worked for Madonna. So she took her. She gets $1,500 a week."

But Ulrike increasingly complained that she felt isolated in Malibu. "He didn't have real friends," Marc Richards, who had been married at the Malibu house, says. "Not even me. There was a hole in him. He tried to fill it with money."