Strange Case of Dr Jekyll and Mr Hyde is the original title of a novella written by the Scottish author Robert Louis Stevenson that was first published in 1886. The original pronunciation of Jekyll was "Jeekul" which was the pronunciation used in Stevenson's native Scotland. The work is commonly known today as The Strange Case of Dr Jekyll and Mr Hyde or simply 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 Edward Hyde.

The work is commonly associated with the rare mental condition often spuriously 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 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.

Stevenson had long been intrigued by the idea of how to incorporate the interplay of good and evil into a story. While still a teenager, he developed a script for a play on Deacon Brodie, which he later reworked with the help of W. E. Henley and saw produced for the first time in 1882. In early 1884 he wrote the short story "Markheim", which he revised in 1884 for publication in a Christmas annual. One night in late September or early October 1885, possibly while he was still revising "Markheim," Stevenson had a dream, and upon wakening had the intuition for two or three scenes that would appear in the story. "In the small hours of one afternoon," says Mrs Stevenson, "I was awakened by cries of horror from Louis. Thinking he had a nightmare, I woke him. He said angrily, 'Why did you wake me? I was dreaming a fine bogey tale.' I had awakened him at the first transformation scene ..."

Lloyd Osbourne, Stevenson's stepson, remembers "I don't believe that there was ever such a literary feat before as the writing of Dr Jekyll. I remember the first reading as if it were yesterday. Louis came downstairs in a fever; read nearly half the book aloud; and then, while we were still gasping, he was away again, and busy writing. I doubt if the first draft took so long as three days".

As was customary, Mrs Stevenson would read the draft and offer her criticisms in the margins. Louis was confined to bed at the time from a haemorrhage. Therefore, she left her comments with the manuscript and Louis in the toilet. She said that in effect the story was really an allegory, but Louis was writing it as a story. After a while Louis called her back into the bedroom and pointed to a pile of ashes: he had burnt the manuscript in fear that he would try to salvage it, and in the process forcing himself to start over from nothing, writing an allegorical story as she had suggested. Scholars debate whether he really burnt his manuscript. There is no direct factual evidence for the burning, but it remains an integral part of the history of the novella.

Stevenson re-wrote the story in three to six days. A number of later biographers have alleged that Stevenson was on drugs during the frantic re-write, for example William Gray's revisionist history A Literary Life (2004) said he used cocaine, while other biographers said he used ergot. However the standard history, according to the accounts of his wife and son (and himself) who were there, say he was bed ridden and sick while writing it. According to Osbourne, "The mere physical feat was tremendous; and instead of harming him, it roused and cheered him inexpressibly". He continued to refine the work for four to six weeks after the initial re-write.

Strange Case of Dr Jekyll and Mr Hyde was initially sold as a paperback for one shilling in the UK and one dollar in the U.S. Charles Scribner's Sons, the American publisher, issued the book on 5 January 1886, four days before the first appearance of the UK edition issued by Longmans; Scribner's published 3000 copies, only 1250 of them bound in cloth. Initially stores would not stock it until a review appeared in The Times, on 25 January 1886, giving it a favourable reception. Within the next six months close to forty thousand copies were sold. The book's success was probably due more to the "moral instincts of the public" than any perception of its artistic merits; it was widely read by those who never otherwise read fiction, quoted in pulpit sermons and in religious papers. By 1901 it was estimated to have sold over 250,000 copies.

Plot - In London, Gabriel John Utterson, a lawyer, is on his weekly walk with his relative Richard Enfield, who proceeds to tell him of an encounter he had some months ago while coming home late at night from Cavendish Place. The tale describes a sinister figure named Mr Hyde who tramples a young girl, disappears into a door on the street, and re-emerges to pay off her relatives with 10 pounds in gold and a cheque signed by a respectable gentleman -- Dr Henry Jekyll, a client and friend of Utterson's -- for 100 pounds. Jekyll having recently and suddenly changed his will to make Hyde beneficiary, Utterson is disturbed and concerned about this development, and makes an effort to seek out Hyde. Upon finally managing to encounter Hyde, Utterson is amazed by how ugly the man seems, as if deformed; though Utterson cannot say exactly how this is so or why it is, Hyde seems to provoke an instinctive feeling of revulsion in him. Much to Utterson’s surprise, Hyde willingly offers Utterson his address. Jekyll tells Utterson not to concern himself with the matter of Hyde.

A year passes uneventfully. One night, a servant girl witnesses Hyde beat a man to death with a heavy cane - MP Sir Danvers Carew, also a client of Utterson. The police contact Utterson, who suspects Hyde of the murder. He leads the officers to Hyde’s apartment, feeling a sense of foreboding amid the eerie weather (the morning is dark and wreathed in fog). When they arrive at the apartment, the murderer has vanished, but they find half of the cane (described as being made of a strong wood but broken due to the beating) left behind a door. It is revealed to have been given to Jekyll by Utterson. Shortly thereafter, Utterson again visits Jekyll, who now claims to have ended all relations with Hyde. Jekyll shows Utterson a note, allegedly written to Jekyll by Hyde, apologizing for the trouble he has caused him and saying goodbye. That night, however, Utterson’s clerk points out that Hyde’s handwriting bears a remarkable similarity to Jekyll’s own.

For a few months, Jekyll reverts to his former friendly and sociable manner, as if a weight has been lifted from his shoulders. Later, Jekyll suddenly begins to refuse visitors, and Dr Hastie Lanyon, a mutual acquaintance of Jekyll and Utterson, dies suddenly of shock after receiving information relating to Jekyll. Before his death, Lanyon gives Utterson a letter, with instructions that he not open it until after Jekyll's death or disappearance. Utterson goes out walking with Enfield, and they see Jekyll at a window of his laboratory; the three men begin to converse, but a look of horror comes over Jekyll’s face, and he slams the window and disappears. Soon afterward, Jekyll’s butler, Mr Poole, visits Utterson in a state of desperation and explains that Jekyll has secluded himself in his laboratory for several weeks, and that now the voice that comes from the room sounds nothing like the doctor’s. Utterson and Poole travel to Jekyll’s house throug