'His fortune,' the magazine stated, 'was the only one of that magnitude ever made in the art market.' A 1998 profile of the family in Vanity Fair magazine asserted that his wealth was estimated at more than $5 billion. As an art dealer Wildenstein was phenomenally successful. A gallery in Tokyo was added in the early 1970s. He took over the running of Wildenstein & Co.'s Paris and New York branches in 1959 and those in London and Buenos Aires in 1963, the year his father died. He had already acted as Group Secretary of the French Pavilion at the World's Fair in 1937 and as exhibitions director at the Jacquemart-Andre Museum. In 1940 Daniel Wildenstein went to New York to work for the family firm. The secrecy attached to these holdings led to a great deal of interest and speculation in the art world. In 1978 Wildenstein & Co's New York storeroom included 20 Renoirs, 25 Courbets, 10 Van Goghs, 10 Cézannes, 10 Gauguins, 2 Botticellis, 8 Rembrandts, 8 Rubens, 9 El Grecos and 5 Tintorettos among a total inventory of 10,000 paintings. Nathan built a huge inventory of European Old Master paintings, sculpture, drawings, furniture and decorative objects, to which Daniel's father, Georges, added Impressionist and Postimpressionist works. The Wildensteins gained a reputation as shrewd businessmen, stockpiling works to maximise their profits when released onto the market. He opened a New York gallery in 1903 and one in London in 1925.

Morgan, Henry Clay Frick, and to the Kress, Rockefeller, and Mellon families. Although he had been working in a tailor's shop when he began to trade in art he proved extremely successful, selling to European collectors such as Edmond James de Rothschild and later to Americans such as J.

He first specialised in 18th-century French painting and sculpture, later expanding to Italian, Dutch, Flemish and Spanish art. Wildenstein's grandfather, Nathan Wildenstein, established an art dealership on the Rue La Boétie in Paris after fleeing his native Alsace during the Franco-Prussian War of 1870/71. He was educated at Cours Hattemer and at the University of Paris, graduating in 1938 and going on to study at the École du Louvre. Wildenstein was born in Verrières-le-Buisson, Essonne, just outside Paris. He was once described as 'probably the richest and most powerful art dealer on earth'. He was the third member of the family to preside over Wildenstein & Co., one of the most successful and influential art-dealerships of the 20th century. Daniel Leopold Wildenstein (11 September 1917 – 23 October 2001) was a French art dealer, historian and owner-breeder of thoroughbred race horses.

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