Cesare Lombroso was an Italian criminologist who founded the Italian School of Positivist Criminology in the 19th century. He developed the theory of atavism, which claimed that criminals have hereditary tendencies that are transmitted genetically and that criminals can be identified by physical abnormalities. Lombroso classified criminals into three categories: hereditary criminals, insane criminals, and criminoids. While his theory of physical criminal types was widely criticized and has been disproven, Lombroso made important contributions by shifting criminology's focus to the individual criminal rather than just their crimes. His work emphasized studying criminals scientifically and treating them individually rather than just punishing their acts.