Nemesis was the goddess of divine retribution and revenge, who would show her wrath to any human being that would commit hubris, i.e. arrogance before the gods. She was considered a remorseless goddess.
Nemesis was widely used in the Greek tragedies and various other literary works, being the deity that would give what was due to the protagonist. She was often called "Goddess of Rhamnous", an isolated place in Attica, where a temple was attributed to her. It was believed that she was the daughter of the primordial god Oceanus. According to Hesiod, though, she was a child of Erebus and Nyx.
One myth concerning Nemesis is that of Narcissus. He was a young man who was very arrogant and disdained those who loved him. Nemesis led him to a pool, where he saw his reflection and fell in love with it. Unable to abandon his reflection, he died there. According to another myth, Nemesis created an egg, from which two sets of twins hatched; one set was Helen of Troy and Clytemnestra, and the other was the Dioscuri.