Johann Christian Heinroth (1773–1843) was probably the world’s first university professor in the field of psychiatry, and he represented a group of contemporary authors in psychiatry designated as “mentalists” (Psychiker), in opposition to the “somaticists” (Somatiker). He is also assumed to have been the first who used the term “psychosomatic.” The present contribution describes Heinroth’s career, his conceptualization of the nature of the human being, the intrinsic relation between body and soul, the etiology of mental disorders, and features of his practical work, particularly on criminal psychology and forensic psychiatry. The contribution further addresses Heinroth’s ideas about the tripartite, hierarchical inner structure of the psyche, and his concept of “person” as a psychological unit that integrates psyche and soma, which implies that mental disorders always affect the integrated unity of body and soul. Finally, some political implications of Heinroth’s anthropological and psychiatric conceptualizations are described.