The Erinyes

The Erinyes, also known as the Eumenides (commonly known in English as the Furies), are chthonic goddesses of vengeance in ancient Greek religion and mythology. A formulaic oath in the Iliad invokes them as "the Erinyes, that under earth take vengeance on men, whosoever hath sworn a false oath". Walter Burkert suggests that they are "an embodiment of the act of self-cursing contained in the oath". They correspond to the Dirae in Roman mythology. The Roman writer Maurus Servius Honoratus wrote (ca. AD 400) that they are called "Eumenides" in hell, "Furiae" on Earth, and "Dirae" in heaven. Erinyes are akin to some other Greek deities, called Poenai.
According to Hesiod's Theogony, when the Titan Kronos castrated his father, Ouranus, and threw his genitalia into the sea, the Erinyes (along with the Giants and the Meliae) emerged from the drops of blood which fell on the Earth (Gaia), while Aphrodite was born from the crests of sea foam. Pseudo-Apollodorus also reports this lineage. According to variant accounts they are the daughters of Nyx ("Night"). while in Virgil's Aeneid, they are daughters of Pluto (Hades) and Nox (Nyx). In some accounts, they were the daughters of Euronymè (a name for Earth) and Kronos, or of Earth and Phorcys (i.e. the sea). In Orphic literature, they are the daughters of Hades and Persephone.
However, in world their origins are yet to be defined as each of these sisters, Alecto, Megaera and Tisiphone, have only been interacted with once. They were met by Oto during his journey through Tartarus. He was immediately attacked by Tisiphone for being a murderer and left for dead. When he awoke he met with Alecto, who advised him to turn back as he was approaching the "Crooked One", she shows little interest in Oto as they are a creature without any blood to shed and she advises him to meet with her sister Megaera. When Oto meets with Megaera she advises him in the matter of his death as a representative of justice. She says he can give up now and she can take him to the underworld to be judged and sentenced to a place in Hades, or he can try and face the coming challenges face insurmountable pain and misery for the chance of returning to his friends. This is phrased in a question of whether Oto considers himself a monster or not. To which his response is that he is Oto and decides to try and make it out of Tartarus.