Article: Les Demoiselles d'Avignon
Section: Cézanne and Cubism

Question: What is the first Cubist picture?

Both Paul Gauguin (1848–1903) and Paul Cézanne (1839–1906) were accorded major posthumous retrospective exhibitions at the Salon d'Automne in Paris between 1903 and 1907, and both were important influences on Picasso and instrumental to his creation of "Les Demoiselles."
According to the English art historian, collector and author of "The Cubist Epoch", Douglas Cooper, both of those artists were particularly influential to the formation of Cubism and especially important to the paintings of Picasso during 1906 and 1907. Cooper goes on to say however "Les Demoiselles" is often erroneously referred to as the first cubist painting.
He explains, 
The "Demoiselles" is generally referred to as the first Cubist picture.
This is an exaggeration, for although it was a major first step towards Cubism it is not yet Cubist.
The disruptive, expressionist element in it is even contrary to the spirit of Cubism, which looked at the world in a detached, realistic spirit.
Nevertheless, the "Demoiselles" is the logical picture to take as the starting point for Cubism, because it marks the birth of a new pictorial idiom, because in it Picasso violently overturned established conventions and because all that followed grew out of it.
Although not well known to the general public prior to 1906, Cézanne's reputation was highly regarded in avant-garde circles, as evidenced by Ambroise Vollard's interest in showing and collecting his work, and by Leo Stein's interest.
Picasso was familiar with much of Cézanne's work that he saw at Vollard's gallery and at the Stein's.
After Cézanne died in 1906, his paintings were exhibited in Paris in a large scale museum-like retrospective in September 1907.
The 1907 Cézanne retrospective at the Salon d'Automne greatly impacted the direction that the avant-garde in Paris took, lending credence to his position as one of the most influential artists of the 19th century and to the advent of Cubism.
The 1907 Cézanne exhibition was enormously influential in establishing Cézanne as an important painter whose ideas were particularly resonant especially to young artists in Paris.
Both Picasso and Braque found the inspiration for their proto-Cubist works in Paul Cézanne, who said to observe and learn to see and treat nature as if it were composed of basic shapes like "cubes, spheres, cylinders, and cones."
Cézanne's explorations of geometric simplification and optical phenomena inspired Picasso, Braque, Metzinger, Gleizes, Delaunay, Le Fauconnier, Gris and others to experiment with ever more complex multiple views of the same subject, and, eventually to the fracturing of form.
Cézanne thus sparked one of the most revolutionary areas of artistic enquiry of the 20th century, one which was to affect profoundly the development of modern art.
Picasso drew each of the figures in "Les Demoiselles" differently.
The woman pulling the curtain on the far right is rendered with heavy paint.
Composed of sharp geometric shapes, her head is the most strictly cubist of all five.
The heads of the crouching figure underwent at least two revisions from an Iberian figure to its current state.
Much of the critical debate that has taken place over the years centers on attempting to account for this multiplicity of styles within the work.
The dominant understanding for over five decades, espoused most notably by Alfred Barr, the first director of the Museum of Modern Art in New York City and organizer of major career retrospectives for the artist, has been that it can be interpreted as evidence of a transitional period in Picasso's art, an effort to connect his earlier work to Cubism, the style he would help invent and develop over the next five or six years.