This chapter explores the multifaceted life of Oskar Lange (1904–1965), a Polish economist, diplomat and socialist thinker whose intellectual and political trajectory spanned continents and ideological divides. Born into a bourgeois German-Polish family, Lange’s early engagement with Marxism and patriotism shaped his academic and political pursuits. Despite obstacles in interwar Poland’s conservative academic climate, he emerged as a leading economist, contributing to business cycle theory and socialist economic models. His 1930s exile in the United States saw him rise to prominence at the University of Chicago, where he engaged with figures like Knight and mentored future economists such as Hyman Minsky. Lange’s diplomatic efforts during the Second World War, including negotiations with Stalin and advocacy for a socialist Poland, underscored his commitment to bridging Eastern and Western blocs. Post-war, he returned to Poland, navigating Stalinist repression before promoting market socialism during the 1956 thaw. The chapter highlights Lange’s unwavering socialist ideals, scientific rigour and patriotism, challenging reductive Cold War narratives. By synthesising archival material and political writings, it presents a nuanced portrait of Lange as a ‘Renaissance man’ whose life encapsulated the tensions between ideology, academia and statecraft in the twentieth century.