The book is dedicated to the outstanding scientist and public figure of Russia, academician David Borisovich Ryazanov (1870-1938). For almost six decades, this name was forbidden to even mention. A thorough biographical sketch based on a wide range of sources allows readers to get an idea of ​ ​ all stages of the life and work of a scientist who managed to do a lot for Russian science in the most difficult conditions of the civil war and the Bolshevik dictatorship, to protect compatriots from the arbitrariness of the authorities.