Jekyll and Hyde

Etymology
From  (1886) by.

Noun

 * 1) Someone or something that has two sides: one good (the "Dr. Jekyll") and one bad (the "Mr. Hyde").
 * 2) * 1944, United Air Lines, Inc, Before the Civil Aeronautics Board: Briefs, Exhibits, etc. (page 28)
 * The public will be better off if United and Western are true competitors, instead of a pair of Jekylls and Hydes.