The Furies were the three goddesses
of vengeance: Tisiphone (avenger of murder), Megaera (the jealous) and Alecto
(constant anger). They were also called the Daughters of the Night, but were
actally the daughters of Uranus and Gaea. Another name for them is the
Without mercy, the Furies would punish all crime including the breaking of rules considering all aspects of society. They would strike the offenders with madness and never stopped following criminals. The worst of all crimes were patricide or matricide, and first and foremost, the Furies would punish this kind of crime.
They would also be the guardians of the law when the state had not yet intervened
or did not exist, or when the crime was a crime of ethics and not actual law
. For example, they would protect beggars and strangers, punish those who
stole the birds' young and even look out for the dogs.
Horrible to look at, the Furies had snakes for hair and blood dripping from their eyes. They changed into the Eumenides, protectors of the suppliant, after Athena had made them merciful sparing Orestes, whom they had stalked for a long time after the murder of his mother and her lover.
From these beings we have the words "furious" and "infuriated".