German-American painter and Professor of History of Art. Between 1913 and 1915, he studied at the Berlin Academy, between 1916 and 1920 at the Essen School of Arts and Crafts and the Munich Academy. From 1919 to 1920, he continued his training at the Bauhaus in Weimar, where he taught preliminary courses as from 1922. In 1925, he was made Bauhausmeister. In 1933, he emigrated to the United States where he stayed until 1949, continuing his teaching career at various American universities and institutes. In 1955, he took part in documenta 1 in Kassel and, in 1963, wrote Interaction of Colour. He was interested in geometrical painting, becoming well-known after 1950 through his compositions with squares entitled Homage to the Square. He can be considered one of the precursors of Op and Minimal Art.