Dr. Henry Jekyll and his alternative personality, Mr Edward Hyde, is a fictional character in Robert Louis Stevenson's 1886 novella Strange Case of Dr Jekyll and Mr Hyde.

Biographie

Dr. Henry Jekyll is a "large, well-made, smooth-faced man of fifty with something of a slyish cast", who occasionally feels he is battling between the good and evil within himself, thus leading to the struggle between his dual personalities of Jekyll and Edward Hyde. He has spent a great part of his life trying to repress evil urges that were not fitting for a man of his stature. He creates a serum, or potion, in an attempt to mask this hidden evil within his personality. However, in doing so, Jekyll transforms into Mr. Hyde, a hideous, evil creature without compassion or remorse. Jekyll has many friends and has a friendly personality, but as Hyde, he becomes mysterious and violent. As time goes by, Hyde grows in power. After taking the potion repetitively, he no longer relies upon it to unleash his inner demon i.e., his alter ego. Eventually, Hyde grows so strong that Jekyll becomes reliant on the potion to remain conscious.

Stevenson never says exactly what Hyde takes pleasure in on his nightly forays, generally saying that it is something of an evil and lustful nature. Thus, in the context of the times, it is abhorrent to Victorian religious morality. Hyde may have been reveling in activities that were not appropriate to a man of Jekyll's stature, such as engaging with prostitutes or burglary. However, it is Hyde's violent activities that seem to give him the most thrills, driving him to attack and murder Sir Danvers Carew without apparent reason, making him a hunted outlaw throughout England.

A lawyer named Gabriel Utterson and Dr. Jekyll's butler Mr. Poole end up breaking into Dr. Jekyll's lab. Inside, they find the body of Hyde wearing Jekyll's clothes and apparently dead from suicide. They find also a letter from Jekyll to Utterson promising to explain the entire mystery. Utterson takes the document home where he first reads Lanyon’s letter and then Jekyll's. The first reveals that Lanyon’s deterioration and eventual death resulted from the shock of seeing Mr. Hyde drinking a serum or potion and as a result of doing so, turning into Dr. Jekyll. The second letter explains that Jekyll, having previously indulged unstated vices (and with it the fear that discovery would lead to his losing his social position) found a way to transform himself and thereby indulge his vices without fear of detection. But Dr. Jekyll's transformed personality Mr. Hyde was effectively a sociopath — evil, self-indulgent, and utterly uncaring to anyone but himself. Initially, Jekyll was able to control the transformations, but eventually he would become Hyde involuntarily in his sleep.

At this point, Dr. Jekyll resolved to cease becoming Mr. Hyde. One night, however, the urge gripped him too strongly, and after the transformation he immediately rushed out and violently killed Sir Danvers Carew. Horrified, Dr. Jekyll tried more adamantly to stop the transformations, and for a time he proved successful by engaging in philanthropic work. One day, at a park, he considered how good a person that he had become as a result of his deeds (in comparison to others), believing himself redeemed. However, before he completed his line of thought, he looked down at his hands and realized that he had suddenly transformed once again into Mr. Hyde. This was the first time that an involuntary metamorphosis had happened in waking hours. Far from his laboratory and hunted by the police as a murderer, Mr. Hyde needed help to avoid being caught. He wrote to Lanyon (in Dr. Jekyll's hand), asking his friend to retrieve the contents of a cabinet in his laboratory and to meet him at midnight at Hastie Lanyon's home in Cavendish Square. In Lanyon's presence, Mr. Hyde mixed the potion and transformed back to Dr. Jekyll. The shock of the sight instigated Lanyon's deterioration and death. Meanwhile, Jekyll returned to his home only to find himself ever more helpless and trapped as the transformations increased in frequency and necessitated even larger doses of potion in order to reverse them. It was the onset of one of these spontaneous metamorphoses that caused Dr. Jekyll to slam his laboratory window shut in the middle of his conversation with Enfield and Utterson.

Eventually, the stock of ingredients from which Dr. Jekyll had been preparing the potion ran low, and subsequent batches prepared by Dr. Jekyll from renewed stocks failed to produce the transformation. Dr. Jekyll speculated that the one essential ingredient that made the original potion work (a salt) must have itself been contaminated. After sending Poole to one chemist after another to purchase the salt that was running low only to find it wouldn't work, he assumed that subsequent supplies all lacked the essential ingredient that made the potion successful for his experiments. His ability to change back from Mr. Hyde into Dr. Jekyll had slowly vanished in consequence. Jekyll wrote that even as he composed his letter, he knew that he would soon become Mr. Hyde permanently, having used the last of this salt and he wondered if Mr. Hyde would face execution for his crimes or choose to kill himself. Jekyll noted that, in either case, the end of his letter marked the end of the life of Dr. Jekyll. He ended the letter saying "I bring the life of that unhappy Henry Jekyll to an end". With these words, both the document and the novella come to a close.

The original pronunciation of Jekyll was "Jeekul" which was the pronunciation used in Stevenson's native Scotland. This is also the pronunciation of Gertrude Jekyll.