Nyx

"Of course not. I would not let my horses eat you, any more than I would Akhlys kill you. Such fine prizes, I will kill myself!"

- Nyx threatening Percy and Annabeth Nyx is the goddess of Night. She is a shadowy figure in Greek mythology but from the extracts about her, it can be gleaned that she was a figure of great beauty and power. She was the female personification of the night, and a daughter of Chaos. In her chariot, pulled by two dark horses, she carries the mantle of night, covering the world with her brother/consort's darkness. It is also said by some that she is the goddess of hellhounds. Her Roman form is Nox.

History
Nyx was born directly from Chaos, the protogenos of the lower air and eldest of the immortals. She married another child of Chaos, Erebus, the Primordial god of depth and darkness, and together they had many children. Once, her son Hypnos angered Zeus by putting him to sleep under Hera's orders so she could shower his son Hercules with misfortune while Zeus was asleep. Zeus found out about his involvement and chased Hypnos who quickly fled to his mother, Nyx, whom Zeus obviously respected and feared as he held his anger at bay, not wishing to offend the great goddess. Another myth is that Nyx's daughter, Hemera (day) left Tartarus when Nyx entered it, creating night and day. According to some Greek articles, Chaos did not exist and Nyx was the first divine Entity, promoting her power and importance even more. Her son Moros (Doom) is mysterious as well and is believed to be omniscient, omnipresent, and omnipotent, as he drives all things to their ends. One example is that the Fates, her daughters, serve her.

The House of Hades
Nyx lives in Tartarus, in the Mansion of Night. When Percy Jackson and Annabeth Chase jump off a cliff to get away from Akhyls, they made their way into Nyx's territory. Nyx was described as a churning figure of ash and smoke, as big as the Athena Parthenos statue, but very much alive. Her dress was void black, mixed with the colors of a space nebula, as if galaxies were being born in her bodice. Her face was hard to see except for the pinpoints of her eyes, which shone like quasars. When her wings beat, waves of darkness rolled over the cliffs. She rode in on a chariot that was made out of Stygian Iron pulled by two massive horses that were black except for their silver fangs. Their legs floated in the abyss turning from solid to smoke as they moved. Nyx wanted Percy and Annabeth as her prizes to kill. Annabeth tried to make her feel unimportant by saying they were tourists in Tartarus and had a travel brochure that did not mention her. Nyx showed them how important she was by showing them her children; Greas, Eris, and more minor gods and monsters. Annabeth then asked if she could get a picture of Nyx with her favorite child. Nyx's children then started arguing amongst themselves allowing Percy and Annabeth to make their escape.

Nyx's Children
Nyx had many children:

From Erebus:
 * Hemera (Day)
 * Nyx (Night): essentially a male copy of herself and twin brother to her daughter Hemera.
 * Aether (Light)
 * Epiphron (Prudence)
 * Thanatos (Non-violent death)
 * Hypnos (Sleep)
 * Sophrosyne (Self-control, restraint, discretion)
 * Eleos (Mercy, pity and compassion)

From Partenogenesis (by herself):
 * Hesperides (Nymphs of sunset, in other myths are daughters of Atlas)
 * Momo (Satire)
 * The Moirae (Fates)
 * Apate (Deceit)
 * Ponos (Hard labor)
 * Moros (Doom)
 * Keres (Violent death)
 * Charon (Ferryman of Hades)
 * Philotes (Affection, friendship and sexual intercourse)
 * Geras (Old age)
 * Nemesis (Retribution)
 * Eris (Discord)
 * Oizys (Distress)
 * Styx (Boundary between life and death. In other myths, daughter of Oceanus and Tethys)
 * Akhlys (Misery, controls the Death Mist)

By the blood of Ouranos:
 * Lyssa (Madness)

Abilities

 * Umbrakinesis: As a goddess of night she has divine authority and absolute control over darkness.
 * She is extremely powerful, being the sister of Gaea   and one of the first known deities.
 * Night Empowerment: She's stronger at night or in dark places (e.g. the underworld).
 * Circadian manipulation: Capable of controlling the movement and rotation of planets thus enabling her to change the flow of night and day.
 * Shadow Mimicry: She can morph into (living) darkness/shadow.
 * She can control nocturnal animals.

Trivia

 * Her horses were called Shade and Shadow.
 * The first ruler of the cosmos was Phanes who gave the 'royal scepter' to Erebos and Nyx and together they ruled everything in creation. Later it was given to Gaea and Ouranos (who in this version of the myths is seen as the son of Nyx), after which it went to Kronos and Rhea and eventually ended up with Zeus and Hera.
 * The symbol of Nyx is a star in a crescent moon which is quite similar to the symbol of modern Islam and the flag of modern Pakistan and Turkey.
 * In the Illiad there is a reference to Nyx having power over men and gods alike, and Hypnos seeking refuge with her for he had angered Zeus, even though still angry Zeus let him be for fear of angering Nyx instead.
 * Nyx is never mentioned by name in any of the Percy Jackson and the Olympians books or in The Heroes of Olympus. However, her name is mentioned once in the glossary section of The Lost Hero, under Hypnos' definition.
 * Her Roman form, Nox, is also the name of a spell in the Harry Potter series that creates darkness. This probably more due to the fact that nox is the Latin for "night," rather than named after the goddess.