Diary of a Madman is a 1963 horror film directed by Reginald Le Borg and starring Vincent Price as Simon Cordier, a French magistrate and amateur sculptor who comes into contact with a malevolent entity. The invisible - yet corporeal - being, called a "horla" is capable of limited psychokinesis and complete mind control. Cordier first interacts with the horla when he meets a prisoner who the horla drove to commit murder. The horla possesses the inmate and attempts to kill Cordier, who in self-defense accidentally kills the man. The magistrate inherits the prisoner's troubles as the horla turns its hauntings toward him. As the horla begins to destroy Cordier's life, he fears he is going mad and seeks help from a psychologist, who effectively suggests a hobby. Cordier chooses to pick up his old interest in art, meeting a model along the way. The horla insists the model is not the charming jewel that Cordier sees, but instead a conniving gold digger, and compels Cordier to treat her as such. This sets up a conflict in Cordier, that he might not be the astute judge of character that his title indicates. As his and others' lives are put in jeopardy, he becomes convinced of the horla's existence and decides drastic measures are needed to end the horla's curse.

The screenplay, written by producer Robert Kent, is an adaptation of Guy de Maupassant's short story "Le Horla" ("The Horla"), written in 1887. Kent's rendition is notably divergent from the source material, especially in relation to the religious and moral themes of the film, which contradict not only those of the short story, but Maupassant's as well.

Simon Cordier, a sculptor possessed by an evil spirit, hires a model to pose for him then learns thereafter that she has been brutally murdered. Written by Anonymous

Simon Cordier, a judge, visits a condemned man in his cell who claims he committed the murders he was condemned for, being under the control of an evil spirit - Horla. Under spell he tries to kill the judge, fails and dies. Upon losing its victim, Horla has no choice but to select a new one, the judge. Written by vlady@worldnet.att.net