Answer
The Mad Doctor (1941) features Basil Rathbone as Dr. George W. Hastings, a scientist who becomes obsessed with creating a serum that will grant him immortality. His experiments lead to madness and murder, as he attempts to use his serum on unsuspecting victims. Rathbone's portrayal of the sinister and unhinged scientist showcases his versatility as an actor and his ability to create memorable and chilling characters.