From Wikipedia

The Real Dr. Jekyll And Mr Hyde

Strange Case of Dr Jekyll and Mr Hyde is the original title of a novella written by the Scottish author Robert Louis Stevenson and first published in 1886. The work is commonly known today as The Strange Case of Dr Jekyll and Mr Hyde or Dr Jekyll and Mr Hyde. It is about a London lawyer named Gabriel John Utterson who investigates strange occurrences between his old friend, Dr Henry Jekyll, and the misanthropic Mr Edward Hyde.

The work is known for its vivid portrayal of a split personality, split in the sense that within the same person there is both an apparently good and an evil personality each being quite distinct from the other. The novella's impact is such that it has become a part of the language, with the phrase "Jekyll and Hyde" coming to mean a person who is vastly different in moral character from one situation to the next.

Strange Case of Dr Jekyll and Mr Hyde was an immediate success and is one of Stevenson's best-selling works. Stage adaptations began in Boston and London within a year of its publication and it has gone on to inspire scores of major film and stage performances.