Painter, printmaker. Studied painting in Vienna and Prague from 1900 to 1906. Included in 1908 and 1909 Kunstschau exhibitions of contemporary art, organized by Gustav Klimt and others in Vienna. Shared a studio with Egon Schiele in 1910. In 1912 moved to Berlin and by then was signing works "MOPP." Contributed many drawings to Franz Pfemfert's left-wing periodical Die Aktion. Early work primarily consisted of nervously energetic portraits of Austrian and German literary and cultural elite; after 1914 the depiction of music became his foremost theme, presented in a style increasingly influenced by Cubism and Futurism. Declared medically unfit for military service. In spring 1915 settled in Switzerland, where he lived until 1920s; returned to Berlin, then Vienna in 1930s.
Made approximately one hundred prints. First lithograph, a poster made in 1911 for his exhibition at Galerie Thannhauser in Munich, was banned by police for indecency and brought accusation of plagiarism from Oskar Kokoschka. Relationship then soured with critic Arthur Roessler, formerly his most important patron. In 1912 began etching, which became his preferred printmaking medium; used it for finely detailed portraits and musical scenes.
A homosexual and a Jew, faced persecution from Nazis, who removed his works from German museums in 1937. Emigrated to New York, via Switzerland, in 1938.