Diary of a Madman is a 1963 American horror film directed by Reginald Le Borg and starring Vincent Price, Nancy Kovack, and Chris Warfield.

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 its evil.

[8] Film historian Wheeler W. Dixon praises Vincent Price's "unusually restrained" characterization of Simon Cordier.

A dispute arose during filming between LeBorg and producer Edward "Eddie" Small (uncredited) over the quality of the disembodied voice of the evil spirit that has taken possession of Simon Cordier (Price).

After testing multiple actors, Small substituted LeBorg's choice for one that had a "raspy" voice, to the director's displeasure.

[10] LeBorg reports that he set up all the special effects Diary of a Madman, including the final sequence, in which the Horla is immolated: "[N]othing was animated.

The NYT reviewer describes the evil spirit, the Horla, as "slightly unusual [having] a voice like a toothpaste commercial and a disconcerting giggle."

Nancy Kovak alone is praised as the young model who Price can't decide whether to "sculpt and scalp her.