Art dealer who bought and sold with immaculate timing Giuseppe Nahmad, who has died aged 80, was the patriarchal figure behind a family that accumulated one of the most valuable collections of modern art ever assembled. The influence on the workings of the art market this brought was immense. The business, also comprising his brothers David and Ezra and, more recently, two nephews both named Helly after their grandfather, has "sold more works of art than anybody alive," according to Christopher Burge, honorary chairman of Christie's. But it became even more famous for the pieces it did not sell, putting together an inventory of more than 3,000 works thought to be worth up to $4bn. The art, which includes about 300 pieces by Pablo Picasso worth bout $900m, is kept in a warehouse in the tax-free port of Geneva. It was Nahmad, known as Joe, eldest of the three brothers, who transformed the conventions of art dealership by holding on to works for a lengthy period instead of looking for quick "kills." Essentially he regarded the buying and selling of art as a futures market. That proved to be a spectacularly successful strategy. His early purchases of blue-chip masters of the impressionist and modern period in the 1950s paid off when those works increased manifold in value during subsequent art market booms. But Nahmad sold as voraciously as he bought, establishing a reputation for shrewd timing. He sold aggressively in the inflated Japanese market of the 1980s, only to buy with equal enthusiasm in the wake of the Tokyo crash. "He was always extremely smart and ahead of the curve in knowing when to buy, when to sell and when to hold on," says David Norman, vice-chairman of Sotheby's Americas. He had a mind like a computer; everything was in his head. The family is very close-knit and collaborative - but Joe was at the centre. There was always a call to Joe. He was very attentive to the quality of the work and had an intuitive understanding of work that was undervalued, for example late-period Picasso, which has risen in value over just the last five years. I couldn't name one individual who has had such an impact on the art market. No one could approach Joe for making split-second decisions at auction. Giuseppe Nahmad was born in 1932 in Aleppo, Syria, to a Sephardic Jewish banking family, who moved to Beirut in 1945. He opened his first dealership in 1957 in Milan, where he was followed by his brothers. His fluency in several languages and ability to mix in artistic circles helped him to build a formidable stock of work, which he shuffled around European cities, taking advantage of price differentials. He lived an opulent lifestyle, matching his love of art with a passion for expensive Italian sports cars, and there were rumours of a romance with the film star Rita Hayworth. But he never married; he is survived by six siblings, who attended his funeral in Jerusalem. Nicknamed "Joe Farouk" in reference to the sybaritic Egyptian king of the 1950s, Nahmad was regarded as eccentric in his love of acquisitions. "If Uncle Joe bought a suitcase, he didn't buy just one suitcase; he bought 20," according to the London-based Helly, who runs a Mayfair gallery (the other Helly has a gallery in New York). As his power and influence grew, Nahmad was criticised in the art world for the secretive nature of his operations and was reportedly questioned in more than one country for suspected currency violations (he denied having been jailed in Italy for possessing stolen currency). He was also accused of distorting the market by artificially inflating prices of artists whose work he held, by bidding over the odds for their remaining work at auction. He was, however, lauded for his consistent presence in the art market, even during its lean years. Jeffrey Deitch, a former dealer and current director of the Museum of Contemporary Art in Los Angeles, once described the Nahmads as "like a major brokerage firm in the stock market," adding: "The market needs a force like this to function." In recent years, Nahmad moved to Monaco and became ever more withdrawn, appearing unshaven and in a baseball cap, though continuing to trade in art via computer and telephone from his suite at the Fairmont hotel. In an interview with the Financial Times last year, the London-based Helly Nahmad said his uncle had once been "a big spender but [was] now tight with himself and uncomfortable with happy people." The interview was granted to promote a "coming out" public exhibition of works held by the family in Zurich's Kunsthaus, which for instance included Picasso's "Harlequin with Flowers" (pictured). A second show is planned in Monte Carlo next summer, which may now be dedicated to the collection's founding father.