Zola, Emile (1840-1902) French writer and art critic; school friend of Cézanne. Manet was introduced to Zola in February 1866. Three months later Zola wrote an enthusiastic essay in defense of Manet's work (L'Evénement, May 1866), which he later expanded into a long article (Revue du XIXe Siècle, January 1867). Manet painted this portrait as an expression of his thanks, and it was shown at the 1868 Salon. In 1870-1903 Zola wrote and published his novel series about the Rougon-Macquart family, including 1880 Nana and 1886 The Masterpiece, a critical characterization of Impressionism.
Nana was a character in Emile Zola's eponymous novel Nana. Manet asked Henriette Hauser, a well-known grande coquette (courtesan), to pose for him for this picture. Henriette Hauser was the mistress of the Prince of Orange, and so was nicknamed "Citron" (lemon in French).
Nana was a Parisian courtesan, and the novel is about her life.
See: Edouard Manet Portrait of Emile Zola, Nana.