Art dealers have been variously described as pioneers, impresarios, lice and rogues.
Some of these extraordinary people championed impoverished artists, nurtured new markets and even raised the status of art itself.
Others were accused of keeping shaky accounts, creative repainting and the unscrupulous manipulation of prices.
Among those who have sold art for a living include tailors, spies the occasional anarchist, scholars, aristocrats and merchants.
Philip Hook, Sotheby's senior specialist in impressionist and modern art has written a book Rogues' Gallery, in which we meet some of these colourful characters.
Hook says art dealing goes back to antiquity but it really only got going in the Renaissance, when the notion of painting as genius, rather than skill, came in.
“Dealing became a rather romantic thing, just as much as the painting and with this huge elasticity in price.”
The great modern art dealers were also often pioneers in difficult, new art movements.
“The impressionism movement was not understood by contemporary collectors, so no one bought the impressionists originally and it took a really convinced, really pioneering art dealer called Paul Durand-Ruel who picked up the impressionists.”
Ambroise Vollard was a great supporter of the next generation, including the like of Cezanne and Andre Derain.
Vollard sent Derain to London to paint the Thames in his new expressionist style. Vollard paid for the trip and one of the artist’s greatest works resulted.
And then there was Daniel-Henry Kahnweiler, perhaps the best example of the dealer/proselytizer.
“He got Picasso’s career going and encouraged him into this difficult to understand and difficult to promote cubism.”
Marcel Duchamp, however, described dealers as lice.
“There is always tension between the cost price paid to artist and price a dealer manages to get from the collector when he resells the work.
“It’s shocking for an artist to learn something he’s been paid £500 for had been sold for £2000 the next day.”
A somewhat unsavoury dealer from the early 20th century was Joseph Duveen “an absolutely splendid figure” says Hook. Duveen bought great works from impoverished European aristos and sold them to the nouveau riche.
He had a gift for intelligence gathering, ‘below the stairs’ intelligence secured through bribing servants furnished him with useful titbits about his clients.
This worked particularly well with a figure in Paris called the Baron Maurice de Rothschild who was incredibly rich but notoriously moody.
“Duveen discovered the Baron suffered cruelly from constipation, so he never offered for sale a painting without first calling through to his valet de chambre to see if the Baron’s bowels had moved that morning.”
Art dealers will always have a certain mystique, he says.
“What you’ve got to understand about art dealers is that they are selling this unique commodity with a value of disconcerting elasticity, what’s being sold is the heady mixture of aesthetic and intellectual stimulation, of spiritual benefit and then things like status and indeed even investment opportunity and this permits the dealer a certain romanticism.”