Justin K. Thannhauser was the son of renowned art dealer Heinrich Thannhauser, who founded the Galerie Moderne in Munich in 1909. From an early age, Thannhauser worked with his father, building an impressive program of exhibitions of Impressionism and Post-Impressionism and the art of the contemporary French and German avant-gardes. The Thannhausers’ commitment to promoting artistic progress paralleled the vision of Solomon R. Guggenheim. In recognition of this shared spirit, Justin Thannhauser ultimately bequest a significant portion of his art collection—including masterpieces by Cézanne, Gauguin, Manet, Monet, Picasso, Pissarro, Renoir, and Van Gogh—which is on view in a dedicated gallery, to the Guggenheim Museum.