Nyx

Nyx was the Greek primordial goddess of the night. A shadowy figure, Nyx stood at or near the beginning of creation and was the mother of other personified deities. Her appearances are sparse in surviving mythology, but reveal her as a figure of such exceptional power and beauty that she is feared by Zeus himself. She is found in the shadows of the world and only ever seen in glimpses.

In Roman mythology, Nyx's equivalent was Nox.

Hesiod
In Hesiod's Theogony, Nyx was born of Chaos. With Erebus, Nyx gives birth to Aether and Hemera. Later, on her own, Nyx gives birth to Moros, the Keres, Thanatos, Hypnos, the Oneiroi, Momus, Oizys, the Hesperides, the Moirai, Nemesis, Apate, Philotes, Geras, and Eris.

In his description of Tartarus, Hesiod locates there the home of Nyx and the homes of her children, Hypnos and Thanatos. Hesiod says further than Hemera leaves Tartarus just as Nyx enters it; continuing cyclicly, when Hemera returns, Nyx leaves.

Homer
In the Iliad, Hypnos is said to have tricked Zeus at the request of Hera. When Zeus found out, he chased Hypnos and he ran to his mother, Nyx. Zeus was scared of Nyx and allowed Hypnos to go unpunished.