Nemesis

In Greek mythology, Nemesis (Greek, Νέμεσις), also called Rhamnousia/Rhamnusia ("the goddess of Rhamnous") at her sanctuary at Rhamnous, north of Marathon, was the spirit of divine retribution against those who succumb to hubris (arrogance before the gods). The Greeks personified vengeful fate as a remorseless goddess. The name Nemesis is related to the Greek word νέμειν [némein], meaning "to give what is due". The Romans equated the Greek Nemesis with Invidia.

"Nemesis" is now often used as a term to describe one's worst enemy, normally someone or something that is the exact opposite of oneself but is also somehow similar. For example, Professor Moriarty is frequently described as the nemesis of Sherlock Holmes.