An enemy, especially an archenemy.
The personification of the "fatal flaw" of a dramatic hero in the style of Greek tragedy.
The principle of retributive justice.
A punishment or defeat that is deserved and cannot be avoided; (an instance of) retribution.
A person or character who specifically brings about the downfall of another person or character, as an agent of that character's fate or destiny, especially within a narrative.
Polar opposite, especially of a literary character.