Walter Benjamin was a 20th century German philosopher and cultural critic affiliated with the Frankfurt School. Some of his major works examined how mechanical reproduction impacted the authenticity and aura of art, how sense perception changed with modernity, and the ambiguous political effects of these changes. His influential 1940 work "Theses on the Philosophy of History" presented an allegory of Paul Klee's painting "Angelus Novus," depicting the angel of history looking backward at a growing pile of wreckage produced by "progress."