Which American painter is famous for the portrait titled, Madame X?

Madame X or Portrait of Madame X is the informal title of a portrait painting by John Singer Sargent of a young socialite named Virginie Amélie Avegno Gautreau, wife of Pierre Gautreau. The specific model was an American expatriate who married a French banker, and became notorious in Parisian high society for her beauty and rumored infidelities. She wore lavender powder and prided herself on her poise and appearance.

For Sargent, the scandal resulting from the painting's controversial reception at the Paris Salon in 1884 amounted to the failure of a strategy to build a long term career as a portrait painter in France. But, it may have helped him in establishing a good and successful career in Britain and America. During his career, he created roughly 900 oil paintings and more than 2,000 watercolors.