"The Strange Case of Dr Jekyll and Mr Hyde" is a novella written by Robert Louis Stevenson that was first published in 1886. It is about a London lawyer named John Gabriel Utterson who investigates strange occurrences between his old friend, Dr Henry Jekyll, and the misanthropic Edward Hyde.
The work is commonly associated with the rare mental condition often called "split personality", wherein within the same person there are at least two distinct personalities. In this case, the two personalities in Dr Jekyll are apparently good and evil, with completely opposite levels of morality.
The Strange Case of Dr Jekyll and Mr Hyde was an immediate success and is one of Stevenson's best-selling works.