1. Nemesis
ΝΈμεσις - Νέμεσις
Reeves Harvey

2. Classical Use Nemesis was the goddess of divine retribution.
Daughter of Nyx, sometimes said to be daughter of Erebus
Punished mortals for crimes, acting in arrogant ways, or for challenging the gods.
Another name for Nemesis is Adrasteia, meaning "the inescapable“
Nemesis and her siblings are gods that personify actions or feelings felt by humans. Thanatos : Death, Hypnos : Sleep, Moros : Doom, Momus : Blame
Nemesis is sometimes said to be daughter of Zeus or Oceanus.
Painting is Nemesis, by Alfred Rethel (1837)

3. Classical Use
By some accounts, Nemesis is the mother of Helen of Troy.
Nemesis punished the hunter Narcissus for being arrogant.
The word nemesis originally meant distributor of fortune, good or bad, but evolved to the meaning of justice or righteous punishment.
Zeus wanted Nemesis but she did not want to be with him so she turned into a goose, but then Zeus turned into a swan and raped her, then she laid an egg with Hellen inside. This egg is then given to Leda, Hellen’s usual mother.
Narcissus was too beautiful and arrogant, he was mean to Echo and so Nemesis cursed Narcissus such that he fell in love with a reflection of himself and died at a pond, turning into the narcissus flower.
Nemesis believed that no one should ever have too much goodness in their lives, and cursed those who were blessed with countless gifts.
Painting is Justice (Dike, on the left) and Divine Vengeance (Nemesis, right) are pursuing the criminal murderer. By Pierre-Paul Prud'hon, 1808

4. Modern Use
Currently holds similar meaning to classical use, a nemesis is a long-standing enemy who wants to cause your downfall.
In the Resident Evil 3 game, a character called The Nemesis is the main villain and seeks to destroy the player.
Nemesis is also a novel by Isaac Asimov.
Modern usage can be seen as meaning what the god Nemesis was to mortals, inescapable vengeance that will usually do something detrimental to you.