William Herbert Sheldon, Jr. (November 19, 1898 – September 17, 1977) was an American psychologist, numismatist, and eugenicist.

He created the field of somatotype and constitutional psychology that correlate body types with temperament, illustrated by his controversial Ivy League nude posture photos.

[3][4] Gaining a two-year fellowship in Europe allowed him to study under Carl Jung, and visit Sigmund Freud and Ernst Kretschmer.

[4][5] In psychology, he developed a new version of somatotypology by classifying people into endomorphic, mesomorphic, and ectomorphic types, based on many photographs and measurements of nude figures at Ivy League schools.

By using body measurements and ratios derived from nude photographs, Sheldon believed he could assign every individual a three-digit number representing the three components, components that Sheldon believed were inborn -- genetic -- and remained unwavering determinants of character regardless of transitory weight change.

"[1] Sheldon also argued that physique was closely correlated with temperamental viscerotonic patterns that powerfully influenced attitudes to food, comfort and luxury, ceremoniousness, sociability, nostalgia, pain, and a great variety of other aspects of human experience.