Dr. Jekyll and Mr. Hyde are two—or one, depending on how you look at it — characters in an 1886 novel by Robert Louis Stevenson, The Strange Case of Dr. Jekyll and Mr. Hyde. The novel is considered a classic of Victorian literature and a harrowing allegory about the duality of human nature, and in most English speaking nations, Dr. Jekyll and Mr. Hyde are familiar literary figures. Psychologists often use the story to illustrate the symptoms of dual personality disorder; Dr. Jekyll is the original, or neutral personality, while Mr. Hyde is a secondary and evil personality.
The basic plot of Stevenson's book is that Dr. Jekyll becomes curious about human nature, and obsessed with the idea that every person actually contains two people; an angel, and a demon. In an attempt to isolate these two personalities, Jekyll develops a potion which brings out the personification of evil in himself: Mr. Hyde. He looks physically different than Dr. Jekyll, with a smaller, twisted body which is in keeping with Victorian notions about physical appearance and moral ability.
Whilethe shape shifting is at first undertaken as a scientific experiment, he begins to be obsessed with the character of Hyde. In the guise of Mr. Hyde, he wanders the streets committing various heinous crimes, ultimately murdering someone and discovering that he cannot turn back into himself without a counter potion. He takes the counter potion to conceal his identity from authorities, but ultimately runs out of the supplies needed to make it and realizes that he is doomed to life as Mr. Hyde, so kills himself in his laboratory.
The Strange Case of Dr. Jekyll and Mr. Hyde addresses a number of themes, not just about good and evil but about Victorian society in general. Victorian life tended to be very dualistic, with heavy social expectations placed on prominent members of society such as doctors. As Mr. Hyde, Jekyll could live out his socially inappropriate fantasies: and this ability ultimately consumed the otherwise neutral character. We are never shown the purely angelic side of his personality, suggesting that perhaps the only personality embedded deep within us is a violent and animalistic one, aware of moral codes but choosing not to obey them.
Someone who experiences violent mood swings or behaves erratically is sometimes said to have a Jekyll and Hyde personality, in reference to the book. Even those who have not read Stevenson's book are familiar with the characters, because they have pervaded popular culture thanks to the book itself in conjunction with stage and film adaptations. The book is often required reading for students to get them thinking about human nature, Victorian society, and what makes a book an enduring classic.