William Sheldon was an American psychologist and physician, best known for his theory of body types, which he developed in the 1940s. He categorized human physiques into three main types: ectomorph, mesomorph, and endomorph. Sheldon believed that these body types were linked to personality traits and behaviors, suggesting that physical characteristics could influence psychological aspects of individuals. In addition to his work on body types, Sheldon was also involved in the study of somatotypes and their relation to criminal behavior. His research aimed to understand how physical form could correlate with various psychological and social outcomes, contributing to the fields of psychology and sociology.