Karl Kleist (1879-1960) was instrumental in pioneering German neuropsychiatry and neuropsychology, including the description of frontal, constructional, limb-kinetic (innervatory) and psychomotor apraxias, frontal akinesia and aspontaneity, as well as object and form blindness. Besides isolating episodic twilight states, involutional paranoia and symptomatic (especially influenza) psychoses, he was particularly involved in applying Wernicke's syndromatic and Kraepelin's prognostic and aetiological principles to classify "neurogenous" psychoses by refuting the assumption of mixed entities whenever possible. Thus, has phasophrenias denoted manic-depressive illness, unipolar affective disorders and marginal, i.e., atypical psychoses. The rather benign cycloid psychoses form the most prominent examples of the latter. Schizophrenias, on the other hand, were limited to poor long-term catamnestic outcomes. Kleist conceptualized the core group of schizophrenic illness as psychic system diseases-hence the origin of the term "systematic schizophrenias" within the Wernicke-Kleist-Leonhard School. Kleist was mainly influenced by Wernicke and his psychic reflex arc, but Ernst Mach's empiriocriticism, Theodor Meynert's cerebral connectionism, and associationism also shaped his outlook. Kleist's localization of cerebral functions by lesion analyses was indeed the best available at the time and continues to reveal insights to the interested reader. From his Frankfurt School, which may have been the last of a completely unified neuropsychiatry, came sound representatives of psychiatry, neurology and neurosurgery. His technical mastery and achievements seem indisputable, but his balancing acts during the Third Reich may today be questioned. Despite joining the National Socialist German Workers' Party (NSDAP) and the local Court of Genealogical Health (Erbgesundheitsgericht), Kleist was, however, one of the few German physicians who continued to treat Jewish patients, to employ Jewish colleagues and to voice evident criticism of the policies of "eugenics" and "euthanasia". This paper attempts to illuminate Kleist's biography and life's work in the relevant historical context.