The Strange Case of Dr Jekyll and Mr Hyde was a 19th century novel 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 referenced the story, when recalling his actions after his Ethical subroutines were removed, noting he was disturbed that all it took was "a flick of the switch to turn (him) in to Mr. Hyde." (VOY: "Equinox, Part II")
The novel was written by Robert Louis Stevenson.