John Bates Clark was an American adherent of the marginalist school who engaged the Austrians and learned from them. He delivered many blows against the historical school in favor of the idea of pure theory. He was also a prominent advocate of free markets in a time when the economics profession was embracing Progressivist ideology. Clark contributed to laying the foundation of what would later become a distinctly American Austrian School. Mises himself regarded him as an outstanding economist, perhaps his favorite American economist.