Hervey Cleckley was an American psychiatrist known for his work on psychopathy. He authored the influential book, The Mask of Sanity, published in 1941, which detailed the characteristics of psychopathic behavior. Cleckley's observations helped shape the understanding of this personality disorder and its impact on individuals and society. Cleckley's research emphasized the distinction between outward charm and inner emotional emptiness in psychopaths. His work laid the groundwork for future studies in psychology and criminology, influencing both clinical practices and the portrayal of psychopathy in popular culture, including literature and film.