M. A. Kosoi - a mason, a heretic and an ober-fiscal

The article is devoted to the particulars of the peculiar biography of M. A. Kosoi, a prominent figure in the Russian fiscal service in the first quarter of the 18th century. The article is the first to describe the service and the criminal activity of Michael Kosoi. His connections in the government are reviewed. Extensive data are provided on the criminal prosecution of M. A. Kosoi in 1725-1727 and on his heretical views in 1728-1729.