Manchurian candidate?
Or Dissociative Identity Disorder (Multiple Personality Disorder)? Via induced trauma where the original nice guy personality is not even aware of a trained assassin personality (or sexually abused personality) existence in the person. And likely neither are the person’s family or friends etc. aware of the one of many personalities split from the original on purpose and for purposes of evil.
Until a triggering sign, word(s), tone, time or code etc. is given causing one of the evil personalities to come to the surface for a time.
I am not sure if this is same as Manchurian candidate but it seems very similar. It is reported we have a fourth generation of these programmed people with sodomized kids as young as eight years old showing split personalities in America. One researcher mentioned an estimated 10 million in America including all four generations starting with the first generation who are in their 60s and 70s now (if alive still).
.
.