A quick trawl through a few numbers explains why. From 1891-1922 the French dealer bought around 12,000 pictures: about 1500 by Renoir, more than 1000 by Monet, 800 by Pissarro, around 400 by Degas and the same number by Sisley and Mary Cassatt.
An exhibition opening this week at the National Gallery forms a chronological survey of Durand-Ruel's career. Inventing Impressionism surveys a highly popular subject through the commercial prism of the art dealer who put the Impressionists on the map and made their fortunes.
The gallery is the second of three venues for this show, which started at the Musée du Luxembourg in Paris and moves to the Philadelphia Museum of Art after London. Slight variations distinguish each display, but the overall aim is to bring together as many Impressionist works as possible that passed through Durand-Ruel's hands.
The dealer first met Monet and Pissarro in London in 1870 when the artists were relatively unknown and had moved to the city to escape the Franco-Prussian War. He went on to skilfully promote their work, and that of their fellow Impressionists, to a wider world in a series of exhibitions seen as ground-breaking at the time.
Now regarded as one of first Modern art dealers, he turned his Paris business into a global firm with branches in London, Brussels and New York.
The National Gallery show starts with a focus on the dealer's home, his early art-dealing career and links with the Impressionists. It moves on to the strategies used to promote their work and ends with an evocation of an exhibition he created at London's Grafton Galleries in 1905, which remains the largest show of Impressionist painting ever attempted.
The 85 works used to create Inventing Impressionism come from public collections around the world and, as so often with 'blue-chip' survey shows of this type, provide a valuable opportunity to see many works seldom shown together from different sources.
Among the highlights, for example, will be all three of Renoir's Dances, famous early 1880s examples of the artist's work. Dance à Bougival from the Museum of Fine Arts in Boston and Danse à la ville and Danse à la campagne from the Musée D'Orsay will appear together in the UK for the first time since 1985. The show reunites five of Monet's Poplars paintings, one of the many series for which the artist became renowned.
• Inventing Impressionism runs from March 4-May 31 in London and continues as Discovering the Impressionists at the Philadelphia Museum of Art from June 24-September 13.