"Professor Unrat" is a novel written by German author Heinrich Mann in 1905. The story revolves around a strict and disillusioned schoolteacher named Professor Unrat, who becomes infatuated with a cabaret singer named Rosa Fröhlich. His obsession leads him to abandon his moral principles and ultimately results in his downfall. The novel explores themes of societal hypocrisy, the conflict between personal desires and social expectations, and the consequences of obsession. It has been adapted into various films, including the famous 1930 movie "The Blue Angel," which starred Marlene Dietrich and helped launch her international career.