a Jekyll and Hyde

Jekyll and Hyde

A person whose personality drastically changes between good and bad. A reference to the main character in the book Strange Case of Dr. Jekyll and Mr. Hyde by Robert Louis Stevenson. Ever since Kyle became a teenager, he's turned into a real Jekyll and Hyde, and it's impossible to anticipate his mood at any given time.
See also: and, Hyde, Jekyll
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

a ˌJekyll and ˈHyde

a person with two separate personalities or ways of behaving, one good, pleasant, etc. and one evil, unpleasant, etc: He’s a real Jekyll and Hyde. At home he shouts at his wife and children all the time; at work he’s always charming and friendly.This comes from a story by Robert Louis Stevenson, Dr Jekyll and Mr Hyde, in which Dr Jekyll takes a drug which separates the good and bad sides of his personality into two characters. All the negative aspects go into the character of Mr Hyde.
See also: and, Hyde, Jekyll
Farlex Partner Idioms Dictionary © Farlex 2017
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References in periodicals archive ?
"It was a game of two halves, a Jekyll and Hyde performance.
"Funke would refer to him as a Jekyll and Hyde because of his sudden outbursts.
At least once a week, usually more often, a patient in my clinic describes himself to me as a Jekyll and Hyde. The assumption always is, of course, that the Jekyll is the real him or her, while the Hyde is an intruder, alien, or interloper.
The transformative effect, however, is not purely pharmacological: for many a Jekyll and Hyde has told me that a quantity of alcohol taken as beer does not have the terrible consequences for his character as the same quantity taken as whisky.
I've heard "He's a Jekyll and Hyde character" as often as I've heard "I'm a Jekyll and Hyde character."
As for the person who claims that her lover is a Jekyll and Hyde, the metaphor serves to preserve and justify her love for him, despite all the evidence that he is unworthy of it.
Having a split personality, schizophrenia, is not a splitting of the personality into multiple parts, not a Jekyll and Hyde phenomenon, despite the popular hold of the Robert Louis Stevenson story.
A woman accused of killing her taxi driver husband told police he could be like a Jekyll and Hyde character after he had been drinking.
You said earlier he can be a Jekyll and Hyde. Is it the drink that changes him?"