nemesis

Short definition from Wiktionary

Noun

1. 1
   An enemy, especially an archenemy.
2. 2
   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.
3. 3
   The personification of the "fatal flaw" of a dramatic hero in the style of Greek tragedy.
4. 4
   Polar opposite, especially of a literary character.
5. 5
   The principle of retributive justice.
6. 6
   A punishment or defeat that is deserved and cannot be avoided; (an instance of) retribution.

Proper noun

1. 1
   The goddess of divine retribution.
2. 2
   128 Nemesis, a main belt asteroid.
3. 3
   A hypothetical star postulated to be orbiting the Sun to explain a perceived cycle of mass extinctions in the geological record.