This 1931 version of RL Stevenson's classic novel is definitive for three main reasons; the amazing, innovative transformation of Jekyll into Hyde; its fabulously salacious pre-code content; and for the astonishing camera movement and POV tracking shots. That Rouben Mamoulian manages such fluidity in the era of camera booths is a miracle.
Credit for the above should be extended to cinematographer Karl Struss. They create incredible close ups and impressionistic images that mirror the hero's duality. There is also a wonderfully atmospheric pictorial of Victorian London, all candle and lamplit shadows and cobbled streets in the rain.
Fredric March deservedly won an Oscar for his split performance, but Miriam Hopkins steals the film as the Cockney sex worker living in terror of Hyde's brutality. Stevenson wrote a story about the ego versus the id, but it was Paramount that added the sexual motifs that still feel transgressive. It is a fetishistic film. The Hays office cut a lot of this for its reissue.
It presents a paradox: that Victorian sexual prohibition drove men to the services of prostitutes; but without these restrictions, man's animalistic nature is capable of terrible depravity. Eventually we see Jekyll as Hyde's mask, sanctimoniously obscuring his real nature and using it to mediate with a hypocritical society. It is one of the most brilliant films of precode Hollywood.