Dr. Renault's Secret - 1942 - J. Carrol Naish, George Zucco

A young man visits his fiancée in a remote French villa where her scientist father resides. There he meets Noel, Dr. Renault's mysterious assistant, who has a strange attraction to Renault's daughter. Soon he learns Noel's true identity: he is an ape that was turned into a man by Renault's bizarre experiments!