It is I who exists, Dr. Jekyll, not you! It is I who shall be rid of you!
~ Sister Hyde

Sister Hyde was the titular villainess and deuteragonist from Dr. Jekyll and Sister Hyde.

She was played by Martine Beswick.

Sister Hyde was the villainous female alter-ego of Dr. Henry Jekyll; the result of Jekyll ingesting an experimental serum that consisted of female hormones. Her appearance is met with jealousy from Susan Spencer, a young woman who fancied Jekyll, until Jekyll referred to his female alter-ego as his widowed sister. The serum was part of Jekyll's experiments that required the use of female cadavers brought in by murderers Burke and Hare, but he later realizes that the bodies need to be fresh, meaning that women have to be murdered.

Jekyll commits the murders himself and hates the concept, but Sister Hyde relishes the killings, and as time passes, her control over Jekyll increases. She even seduces and kills Jekyll's good friend, Professor Robertson, after he asks questions regarding the murders. By this point, Sister Hyde's sinister agenda is clear: she plans to take full control and eliminate her male alter-ego.

In order to complete her villainous plan (as well as adding further insult to injury), the evil Sister Hyde set her sights on killing Susan, who was set to go on an opera date with Jekyll. She followed Susan while she was out on her own and took out her knife with intent on killing her, only to be stopped at the nick of time when Jekyll regains control. In the film's last moments, Jekyll commits another murder in an attempt to hold Sister Hyde at bay, but the police catch up to him, leading to a chase that included Jekyll on the ledge of a building. At that moment, Jekyll transforms into Sister Hyde, and ends up falling off the ledge and dies resembling a deformed male and female hybrid.