German-born art historian, art collector, and one of the most notable French art dealers of the 20th century. He became prominent as an art gallery owner in Paris beginning in 1907 and was among the first champions of Pablo Picasso, Georges Braque and the Cubist movement in art, acting as an art dealer and as a spokesman for Cubist artists. Along with such men as Alfred Flechtheim, Paul Cassirer, Daniel Wildenstein, Léonce Rosenberg and Paul Rosenberg, Kahnweiler was one of the most influential art connoisseurs of the 20th century.
He was among the first people to recognize the importance and beauty of Picasso’s Les Demoiselles D’Avignon (created in 1907) and immediately wanted to buy it along with all of Picasso’s works. Picasso wrote of Kahnweiler, “What would have become of us if Kahnweiler hadn’t had a business sense?” Kahnweiler’s appreciation of Picasso’s talents was especially gratifying to the artist, since he was largely unknown and destitute at the time when many of his most famous works were created.
In his gallery, Kahnweiler supported many of the great artists of his time who found themselves without adequate recognition and little or no interest among collectors. Initial purchases included works by Kees van Dongen, André Derain, Fernand Léger, Georges Braque, Juan Gris, Maurice de Vlaminck and several other artists of the same generation.
Kahnweiler sponsored the first exhibition of the work of Georges Braque. He encouraged the practice of publishing Beaux Livres (beautiful books), in which a contemporary artist would illustrate 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.
The outbreak of World War I in 1914 not only ruptured the Cubist experiments in art, but also forced Kahnweiler to live in exile in Switzerland; due to his German citizenship, he was considered an alien under French law. Many German nationals living in France had their possessions sequestered by the French state, and as a result, Kahnweiler’s collection was confiscated in 1914 and sold by the government in a series of auctions at the Hôtel Drouot between 1921 and 1923.
During the years of exile (until 1920), Kahnweiler studied and wrote works such as Der Weg Zum Kubismus and Confessions esthétiques. Writing becoming a passion he continued over his lifetime, and he authored hundreds of books and major articles. The second period of enforced writing came during a period of internal exile caused by the events of World War II. As a Jew, the Nazis forced him to flee Paris. He remained in France in hiding.
Daniel-Henry Kahnweiler died in Paris on 11 January 1979, aged 94.

Link to Wikipedia biography