Dr. Wilson: Doctor Jekyll, I presume? They found a half-eaten sheep in the zoo, and the police want to ask you a few questions.
The Strange Case of Dr. Jekyll and Mr. Hyde was a story by Robert Louis Stevenson, originally published in 1886. In the tale, Dr. Jekyll, a peaceful man, created a potion that unleashed his "evil side", the murderous Mr. Hyde. Since its publication, the term "Dr. Jekyll and Mr. Hyde" has come into colloquial use, to refer to the good and evil parts of a person.