Paul Durand Ruel: The man who invented impressionism
4 March 2015 Last updated at 00:34 GMT
You might never have heard of Paul Durand Ruel, but you will know the artists the dealer made famous.
Monet, Manet, Pissarro and Degas all have him to thank for backing then when nobody else would, in the process writing the first chapter in the story of modern art.
BBC arts editor Will Gompertz went along to the Inventing Impressionism exhibition at the The National Gallery.
Video journalist: Dan Curtis
Still photograph of Paul Durand-Ruel in his gallery, taken by Dornac, about 1910. Courtesy of Durand-Ruel & Cie.