The Strange Case of Doctor Jekyll and Mister Hyde was a 19th century novel concerning the kindly Dr. Jekyll and his malevolent alter ego Mr. Hyde.
In 2266, Commander Balok of the Fesarius referred to his menacing puppet as "Mr. Hyde to my Jekyll". (TOS: "The Corbomite Maneuver")
In 2376, The Doctor, when recalling his actions after his ethical subroutines were removed, was disturbed that all it took was "a flick of the switch to turn [him) into Mr. Hyde." (VOY: "Equinox, Part II")
The novel was written by Robert Louis Stevenson.