Karl Leonhard (March 21, 1904 in Edelsfeld, Bavaria, Germany — April 23, 1988 in East Berlin, GDR)was a German psychiatrist, who stood in the tradition of Carl Wernicke and Karl Kleist. He created a complex classification of psychotic illnesses called nosological.His work covered Psychology, Psychotherapy, Biological psychiatry and Biological psychology. Moreover he created a classification of Nonverbal communication.

He was born as the sixth of eleven children, his father being a Protestant minister. His medical education (at Erlangen, Berlin and Munich) was completed in 1928 and he worked as a physician at psychiatric hospitals in Erlangen, then a year later Gabersee and from 1936 Frankfurt am Main, to which last he was called by Karl Kleist. During the period of the Third Reich in order to save his patients from being killed by means of the T-4 Euthanasia Program, he stopped making diagnoses that would endanger a patient. In particular he stopped making any diagnoses of schizophrenia.

He became a professor at Frankfurt in 1944 and a professor at Erfurt in the Soviet zone of Germany in 1954. In 1957 he became director of the psychiatric department at the Charité Hospital linked to the Humboldt University in East Berlin. He wanted to move back to West Germany in the sixties, but was refused the permission by the East German authorities. As compensation he got increased support for his scientific work. During his lifetime he interviewed more than 2000 psychotic patients, latterly with Dr Sieglinde von Trostorff.

According to Helmut Beckmann (see "Books" below), editors of Western journals rejected his papers because "they were not in conformity with the standard practice of Anglo-American psychiatry and also because he pursued without compromise his own path derived from his findings." Most of his work was not translated into English. However summaries of Leonhard's views were included by Frank Fish in his "Schizophrenia" of 1962 (2nd edition 1976 ISBN 0-7236-0334-0) and "Clinical Psychopathology" of 1967 (2nd edition 1985 ISBN 0-7236-0605-6) which were widely read, if not understood, in their day.

Today diagnosis for psychotic patients and mentally or otherwise ill persons are most commonly placed by ICD or DSM criteria.Psychosis will in general appear as an affective disorder (e.g. psychotic depression), a form of schizophrenia (e.g. catatonic type of schizophrenia) or a schizophrenia-like disorder, like the schizoaffective disorder for example.