Ernst Kretschmer (8 October 1888 – 8 February 1964) was a German psychiatrist who researched the human constitution and established a typology.

He attended Cannstatt Gymnasium, one of the oldest Latin schools in Stuttgart area.

After he resigned from the AÄGP, he started to support the SS and signed the "Vow of allegiance of the professors of the German universities and high-schools to Adolf Hitler and the National Socialistic state."

Kretschmer is also known for developing (in the first quarter of the 20th century) a classification system that can be seen as one of the earliest exponents of a constitutional (the total plan or philosophy on which something is constructed) approach.

He based his classification system on four main body-types: The concept of two great psychopathological types of manic-depressive or 'circular' insanity and dementia praecox (i. e. schizophrenia) was developed by Emil Kraepelin (1856-1926).

Kretschmer associated each of his body types with certain personality traits and, in a more extreme form, with different mental disorders.

[5] Kretschmer believed that pyknic persons were friendly, interpersonally dependent, and gregarious.

This was seen as a milder form of the negative symptoms exhibited by people with withdrawn schizophrenia.

[citation needed] The essential characteristic of the asthenic type, in Kretschmer's words, is "a deficiency in thickness combined with an average unlessened length".

; cm) Kretschmer's male athletic type is characterized by the strong development of the musculature, skeleton, and skin.

[5] The expression "hypertrophied" means a development which oversteps the average, not in the sense of a pathological disturbance.

; cm) Kretschmer's pyknic type is characterized by the peripheral development of the body cavities (breast, head, and stomach), and a tendency to a distribution of fat about the torso.