Jekyll and Hyde
noun
Je·kyll and Hyde ˈje-kəl-ən-ˈhīd 
also ˈjē-,
or ˈjā-
: one having a two-sided personality one side of which is good and the other evil
Example Sentences
He's a real Jekyll and Hyde who can become violent without warning. his Jekyll and Hyde tendencies
Word History
Etymology
Dr. Jekyll & Mr. Hyde, representing the two-sided personality of the protagonist in The Strange Case of Dr. Jekyll and Mr. Hyde (1886) by R. L. Stevenson
First Known Use
circa 1922, in the meaning defined above