Question: Which type of historian was Kahnweiler?
About the article "Pablo Picasso", section "Rose Period".

Candidate passages:
Daniel-Henry Kahnweiler (25 June 1884 - 11 January 1979), was a German-born art historian, art collector, and one of the premier French art dealers of the 20th century.
He became prominent as an art gallery owner in Paris beginning in 1907 and he was among the first champions of Pablo Picasso, Georges Braque and Cubism. 
"Portrait of Daniel-Henry Kahnweiler" (Spanish: "Retrato de Daniel-Henry Kahnweiler") is a 1910 oil on canvas painting by Pablo Picasso in the Analytical Cubism style.
It was completed in 1910, and is in the collection of the Art Institute of Chicago.
The artwork displays brown as its prominent color, with dimensions 100.5 cm × 73 cm. 
In 1933, he became a partner in the "Mayor Gallery" in London and planned to show works of Picasso, Léger, Miró and Klee in collaboration with Paris-based art dealers like Daniel-Henry Kahnweiler and Pierre Loeb (1897–1964); however, this collaboration ended fast and unfavourably.
Cooper was paid out in works of art.
Cooper attributed this failure not least to the conservative policy of the Tate Gallery; according to Richardson, his resentment was the catalyst for the structure of his own collection, which should prove the backwardness of the Tate Gallery.
At the outbreak of the Second World War 1939, he had acquired 137 cubist works, partly with the help of collector and dealer Dr. Gottlieb Friedrich Reber (1880–1959), some of them masterpieces, using a third of his inheritance. 
The Rose Period (1904–1906) is characterised by a more cheery style with orange and pink colours, and featuring many circus people, acrobats and harlequins known in France as saltimbanques.
The harlequin, a comedic character usually depicted in checkered patterned clothing, became a personal symbol for Picasso.
Picasso met Fernande Olivier, a bohemian artist who became his mistress, in Paris in 1904.
Olivier appears in many of his Rose Period paintings, many of which are influenced by his warm relationship with her, in addition to his increased exposure to French painting.
The generally upbeat and optimistic mood of paintings in this period is reminiscent of the 1899–1901 period (i.e.
just prior to the Blue Period) and 1904 can be considered a transition year between the two periods.
By 1905, Picasso became a favourite of American art collectors Leo and Gertrude Stein.
Their older brother Michael Stein and his wife Sarah also became collectors of his work.
Picasso painted portraits of both Gertrude Stein and her nephew Allan Stein.
Gertrude Stein became Picasso's principal patron, acquiring his drawings and paintings and exhibiting them in her informal "Salon" at her home in Paris.
At one of her gatherings in 1905, he met Henri Matisse, who was to become a lifelong friend and rival.
The Steins introduced him to Claribel Cone and her sister Etta who were American art collectors; they also began to acquire Picasso and Matisse's paintings.
Eventually Leo Stein moved to Italy.
Michael and Sarah Stein became patrons of Matisse, while Gertrude Stein continued to collect Picasso.
In 1907 Picasso joined an art gallery that had recently been opened in Paris by Daniel-Henry Kahnweiler.
Kahnweiler was a German art historian and art collector who became one of the premier French art dealers of the 20th century.
He was among the first champions of Pablo Picasso, Georges Braque and the Cubism that they jointly developed.
Kahnweiler promoted burgeoning artists such as André Derain, Kees van Dongen, Fernand Léger, Juan Gris, Maurice de Vlaminck and several others who had come from all over the globe to live and work in Montparnasse at the time.
Kahnweiler is considered one of the major dealers and spokesmen for Cubism.
He was among the first people to recognize the importance and beauty of Picasso's "Les Demoiselles D'Avignon", immediately wanting to buy it and all of Picasso's works.
Picasso wrote of Kahnweiler "What would have become of us if Kahnweiler hadn't had a business sense?"
– compelling because at the time of the origination of his most famous works Picasso was largely unknown as an artist and destitute.
Kahnweiler supported in his gallery all of his great artists of the time; who had no audience, or collectors, - initial purchases included works by Kees van Dongen, André Derain, Fernand Léger, Georges Braque, Juan Gris, Maurice de Vlaminck and several others of the same generation.
Kahnweiler wanted as he said to "defend" artists he believed in, but only those who had no dealers and whom he believed were great artists.
Rather than exhibiting the popular works of the past and present greats, Kahnweiler championed burgeoning artists such as André Derain, Alberto Giacometti, and others, who had come from all over the globe to live and work in Montparnasse and Montmartre at the time.
Thus Paul Cézanne although a great artist was considered too old to be represented, and his work was being handled by Ambroise Vollard at the time.
Along with such men as Alfred Flechtheim, Paul Cassirer, Daniel Wildenstein, Léonce Rosenberg and Paul Rosenberg, Kahnweiler was one of the influential connoisseurs of the 20th century.
As a businessman Kahnweiler innovated many new ways of working with artists; and art dealing; - now established practice with art dealers.
In 1907 when there were only half a dozen good galleries in Paris, he made contracts with artists to buy all of their work (freeing them from the worry and restraint about cost of living and creating work).
He saw them daily to discuss their work, (they were friends, he co-owned little sailing boats with his artists), he photographed each work, (he felt it imperative to have a record), he held exhibitions of their work and he promoted their work internationally.
Kahnweiler gave the first exhibition of the work of Georges Braque.
He encouraged the practice of "Beau Livres" (beautiful book), where a contemporary artist illustrates a work of a contemporary writer - he expanded his presentations by bringing together artists, writers and poets to produce their works as a joint project in more than 40 books, so Picasso illustrated the works of Max Jacob etc.
In fact as an art and literary publisher he had no equal; being the first to publish works by Max Jacob, Guillaume Apollinaire, André Masson, Gertrude Stein, Pablo Picasso, and many others and in so doing launched many literary careers.
So strong a business ability did Kahnweiler have that by the 1950s his art gallery was in the top 100 companies in France in terms of turnover from export.