Ernst Kretschmer was a prominent German psychiatrist best known for his studies showing a correlation between body type and personality. He earned a doctorate in medicine at the University of Tübingen in 1913 and began a residency in psychiatry. In 1914 he completed a dissertation on the role of delusion in manic depression ( bipolar disorder).

At the beginning of World War I, Kretschmer joined the medical corps of the German Wehrmacht and served at a field hospital, then at a rehabilitation center for emotionally disturbed soldiers. He observed soldiers who suffered shell shock which led to conversion reactions, in which emotional problems took a physical form. He also recorded paranoid reactions that were linked with brain trauma. Based on his observations, he published the monograph Hysteria, Reflex and Instinct in 1923. Kretschmer devised a treatment for military victims of hysteria which involved lying quiet in a dark room and...