William Herbert 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. This classification aimed to link physical characteristics with personality traits and behaviors. Sheldon also conducted research on the relationship between genetics and behavior, contributing to the field of psychology. His work has been influential in both psychology and body image studies, although some of his theories have faced criticism and are considered outdated in modern science.