There have been some memorable characters in fiction - some call them messengers of justice, others call them... serial killers. The shortlisted ones are Dexter Morgan of the TV series Dexter, Yagami Raito of the manga Death Note, and Dr. Hannibal Lecter in the numerous novels and movies featuring him. (Spoilers follow...)
They come from different backgrounds and have their distinctive modus operandi, but they are all hyper-intelligent, meticulous, confident about their abilities, and sociopathic. Very charismatic sociopaths who are (or in the case of Death Note, have been) quite successful in hiding what they do.
(to be continued)