The Doctor's Horrible Experiment, also known as Le Testament Du Docteur Cordelier, is a 1959 French horror film directed by Jean Renoir. It is based on the story "Strange Case of Dr. Jekyll and Mr. Hyde" by Robert Louis Stevenson. The film stars Jean-Louis Barrault as Dr. Cordelier, Teddy Bilis as Maître Joly, and Sylvie Huguel as Jacqueline, a young woman Opale has assaulted.
The film begins with Cordelier, a well-respected neuroscientist, being called to examine a patient who has been having nightmares. But instead of treating the woman, Cordelier hypnotizes her, revealing that she actually enjoyed her nightmares and wants to have more of them. This sets the stage for Cordelier's descent into madness.
As Cordelier continues his research, he begins to experiment on himself, taking a serum that transforms him into a monstrous alter ego named Opale. While in this state, Cordelier attacks and kills a colleague who attempted to blackmail him. Cordelier's will bequeaths his entire estate to Opale, whom he claims is his lawful heir and who flashes through his mind in his alter ego state.
Maître Joly, a close friend of Cordelier, is horrified by the change in his friend and becomes suspicious of Opale, who he learns has been attacking women and children in the area. Joly confronts Cordelier, and in his Opale state, Cordelier confesses to his crimes. When he wakes up, he is shocked by what he has done and begs Joly to turn him over to the authorities. Joly does so, and Cordelier is sent to a mental institution.
The Doctor's Horrible Experiment is a complex and chilling examination of the dark side of humanity and the dangers of unchecked scientific ambition. It was met with mixed reviews upon its release, but has since gained a reputation as one of Jean Renoir's most fascinating and disturbing films.