An intellectually brilliant person who excells at using his or her mental abilities for negative or harmful ends; especially a criminal mastermind .
The spirit each person is believed to have in attendance, according to certain religious or mythological traditions, which tries to negatively influence him, and is opposed by his good genius; loosely, someone who is a bad influence.
A person who exhibits an extraordinary ability in one subject (often mathematics) whilst being intellectually disabled in many other domains.