I found this on the web:   The current term "bipolar disorder" is of fairly recent origin and refers to the cycling between high and low episodes (poles). A relationship between mania and melancholia had long been observed, although the basis of the current conceptualisation can be traced back to French psychiatrists in the 1850s. The term "manic-depressive illness" or psychosis was coined by German psychiatrist Emil Kraepelin in the late nineteenth century, originally referring to all kinds of mood disorder. German psychiatrist Karl Leonhard split the classification again in 1957, employing the terms unipolar disorder (major depressive disorder) and bipolar disorder.   Hope this helps answer  your question!