Krae·pe·lin \ˈkrep-ə-ˌlēn\ , Emil (1856–1926), German psychiatrist. Kraepelin was one of the foremost psychiatrists of his time. In 1883 he published an influential psychiatry textbook that introduced his classification of mental disorders. His system was later modified, but basically it remains in use today. In 1899 he made an important differentiation between manic-depressive psychosis (now usually called bipolar disorder) and schizophrenia. He also made noteworthy pioneering efforts to apply the methods of experimental psychology to clinical study.