First published in 1886, Dr. Jekyll and Mr. Hyde is author Robert Louis Stevenson's classic tale of man's inner struggle between good and evil. The novella revolves around the investigation by London lawyer Gabriel John Utterson, concerning the association between his old friend Dr. Henry Jekyll and the evil, morally corrupt Edward Hyde, to whom Jekyll has recently willed his estate. Through the use of a magic potion, Dr. Jekyll, who nurtured a belief that every person has two distinct personalities, is transformed into Mr. Hyde, in order to indulge in the darker side of his character without any consequences besmirching Jekyll's good name. After some time, Jekyll finds that he is involuntarily turning into Hyde and must use the magic serum, which is running low, in order to turn back. Stevenson from early on in his career was interested in the impact of personality on human behavior and incorporated it into this work. A respected medical practitioner undertaking an experiment to split one person into two different personalities is a classic examination of the duality that exists within man and the tragic consequences that can occur when the darker elements of one's character are let out. "Split personality" is referred to in psychiatry as dissociative identity disorder, where within the same body there exists more than one distinct personality. The phrase "Jekyll and Hyde" has become part of the vernacular to refer to people with an unpredictably dual nature who are vastly different in moral character from one situation to the next.