French art historian, art collector, publisher and one of the most influential French art dealers of the 20th century. The son of a Jewish antique dealer, Alexander Rosenberg, and brother of the gallery owner, Paul Rosenberg (21 rue de la Boétie, Paris), Léonce, a prominent gallery owner in Paris at the end of World War I, would become one of the world’s major dealers of Modern art.
Leaving the family-owned gallery in 1910 Léonce opened his own business called Haute Epoque at 19 rue de La Baume, Paris. As an antiquarian Rosenberg began buying works by Cubist artists. By 1914 his collection included works by Pablo Picasso, Jean Metzinger, Albert Gleizes, Auguste Herbin, and Juan Gris. After serving in World War I (1916-1917) he pursued his interests and represented these and other artists, and by the end of the war opened a new show space, Galerie de L’Effort Moderne.
A veritable center of activity and interest during the rise of modern art, the Galerie de L’Effort Moderne closed permanently in 1941, as a result of anti-Semitic laws and by the threat of the Nazi occupation of France. Eventually, the Nazi authorities looted some of his collection. The gallery was not reopened following the war due primarily to Rosenberg’s death on 31 July 1947 in Neuilly-sur Seine.
Link to Wikipedia biography