Nyx

Nyx was 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. 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 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 Zeus cannot defeat her, another being that the Fates, her daughters, serve her.

Nyx's Children
Nyx had many children:

From Erebus:
 * Hemera (Day) In other myths she is sister of Nyx.
 * Nyx (Night) Essentially a male copy of herself and twin brother to her daughter Hemera.
 * Aether (Light/bright upper air of heaven)
 * 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)
 * Oneiroi (the thousand personifications of the dreams)
 * Keres (fates of violent death)
 * Charon (Ferryman of Hades)
 * Philotes (Affection, friendship and sexual intercourse)
 * Geras (Old age)
 * Nemesis (Retribution)
 * Eris (Discord, though most say she is the daughter of Zeus and Hera)
 * Oizys (Distress)
 * Styx (Boundary between life and death. In other myths its daughter of Oceanus and Tethys)
 * Achlys(Death mist)

By the blood of Ouranos:
 * Lyssa (madness)

Abilities

 * Umbrakinesis: As a goddess of night she has complete dominion over darkness.
 * She is much more powerful than the Titans and Olympians, being the 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

 * 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 tough 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.