From Naruto; it should be Orochimaru.
I like his "curiousity" on existance; and his concept of "questioning". He does not have morals fitting into...anything. He does not have a sense of justice; he just "does", "questions", "experiments", "answers"; just because he can; just because he is willing to and want to. Him seeking the meanings of things related to existance, power, immoratlity revealing many things people are infact question, but refuse to go deeper in those "questionings" because sometimes a human can be afraid of what he can become or the answers he may get. That's why many of us stick and bound to ideaologies, religions, traditions, social norms, cultures; because they are "safe"; they can give "answers" that can seemingly bypass our curiousity. But Orochimaru does not have such so called values. That's why he seeks and questions. It is questionable whether he is "evil" or not; but he is one of the best written characters in the manga...Lets up he did not "turn good" or became Sasuke's *****; such character should not be ruined.