Nemesis is the agent of retribution or downfall that catches up with a character, especially one guilty of hubris. In Greek thought Nemesis was also the goddess who punished presumption.

In literature the nemesis may be a person—an avenger or rival—or a more abstract force of consequence. The tragic hero’s nemesis arrives as the inevitable result of earlier actions or character. In broader usage the word has come to mean a long-standing rival or archenemy, the figure who continually opposes and may ultimately defeat the protagonist. Comic-book and adventure fiction rely heavily on the nemesis as a structural counterpart to the hero.

A satisfying nemesis feels both opposed to the protagonist and somehow bound to them—by history, by similarity, or by the logic of the plot. The final confrontation with the nemesis often coincides with the story’s climax. Whether divine justice or human rival, the nemesis embodies the bill that eventually comes due.

The force or figure that delivers the consequences a character has earned is their nemesis.