Argentinean political philosopher Ernesto Laclau's theory of populism was the first and arguably the most influential attempt to treat populism, not only as an aberrant form of liberalism, but as a logic defining mass political organization and the place of class within it. First published in Politics and Ideology in Marxist Theory (1977), Laclau's definition of populism aimed to formalize the relationship between class and the people, or the ideological and economic determination of politics. The present essay explores populism as a problem for the analysis of twentieth-century cultural forms in Latin America by examining Argentinean artist Antonio Berni's textual and institutional interventions in the mid-1930s. Influenced by David Alfaro Siqueiros's technical innovations and theoretical interventions, Berni was also critical of the technical determinism and abstract universal subject of emancipation that he encountered in the Mexican artist's calls for a “dialectical-subversive” art. The present chapter reconstructs Berni's work as founding director of the atelier and school known as the Mutualidad Popular de Estudiantes y Artistas Plásticos de Rosario and his polemical response to Siqueiros as a way of historicizing the relationship between class and the people at stake in Laclau's formulation.