Probably Jerry Lewis's most enduring film, and the one that sparked a critical reappraisal of his entire ouvre, this variation on The Two Faces of Dr. Jekyll has inspired not only a 1996 Eddie Murphy remake and followup but an animated direct-to-video sequel and a proposed Broadway musical version directed by Jerry with music by the late Marvin Hamlisch. Look for an impossibly young Henry Gibson in a miniscule role in his first feature.