Ludvig Dmitrievich Faddeev (Russian: Людвиг Дмитриевич Фаддеев, translit. Ljudvig Dmitrievič Faddeev) was a Russian theoretical physicist, academician (and many years secretary of the Russian Academy of Sciences), son of the algebraist D. K. Faddeev. With Popov he invented a remarkable method in quantization of gauge theories, i.e. in the evaluation of path integrals with gauge field degrees of freedom (Faddeev-Popov method, see at BRST complex). With B. S. Pavlov, Fadeev has applied the abstract scattering theory to the study of automorphic functions. Faddeev is one of the pioneers of the Leningrad (St. Petersburg) school of integrable systems and quantum inverse scattering method? which also lead to the discovery of quantum groups.