The Strange Case of Doctor Jekyll and Mister Hyde
From Memory Alpha, the free Star Trek reference
The Strange Case of Dr Jekyll and Mr Hyde was a 19th century novel written by Robert Louis Stevenson concerning the kindly Dr. Jekyll and his malevolent alter-ego Mr. Hyde.
Commander Balok of the Fesarius had heard of the novel and referred to his menacing puppet as "Mr. Hyde to my Jekyll". (TOS: "The Corbomite Maneuver")
The Doctor also refrenced the story, when recalling his actions after his Ethical subroutines were removing, noting he was distubed that all it took was "a flick of the switch to turn (him) in to Mr. Hyde." (VOY: "Equinox, Part II")
