Dr. Hervey M. Cleckley was an American psychiatrist known for his influential work in the field of psychology. He is best recognized for his book, "The Mask of Sanity," published in 1941, which provided a detailed study of psychopathy. Cleckley's observations and descriptions of psychopathic behavior have significantly shaped the understanding of this mental health condition. Throughout his career, Cleckley emphasized the importance of clinical observation and the complexities of human behavior. His research contributed to the development of diagnostic criteria for psychopathy and influenced later studies, including those by Robert D. Hare, who further explored the concept of psychopathy in the context of criminal behavior.