Oneiros

In Greek mythology, the Oneiroi or Oneiri, sing. oneiros, (Ὄνειροι, "Dreams") were various gods and demigods that ruled over dreams, nightmares, and oneiromantic symbols.

According to Hesiod, they were the sons of Nyx (Night) and the brothers of Hypnos (Sleep), Thanatos (Death), Geras (Old Age), and other beings, all produced via parthenogenesis.

Cicero follows this tradition, but describes the sons of Nyx as fathered by Erebus (Darkness).

According to Ovid, they were the sons of Hypnos and his wife Pasithea (therefore making them Nyx's and Erebus' grandsons).

Euripides calls them instead sons of Gaia (Earth) and pictures them as black-winged daemons.

They are the dark-winged spirits ( daimones ) of dreams which emerge each night like a flock of bats from their cavernous home in Erebos—the land of eternal darkness beyond the rising sun. The Oneiroi pass through one of two gates ( pylai ). The first of these, made of horn, is the source of the prophetic god-sent dreams, while the other, constructed of ivory, is the source of dreams which were false and without meaning. The term for nightmare is  melas oneiros  (black dream).

According to some the leader of the Oneiroi is Morpheus, a god who appears in the dreams of kings in the guise of a man bearing messages from the gods.

The Latin poet Ovid presents them not as brothers of Hypnos, but as some of his thousand sons. He mentions three/four by name: Morpheus was identified as the god of dreams, Phobetor as the god of nightmares, Icelos/Ikelos as the god of people in prophetic dreams, and Phantasos as the god of inanimate objects in Prophetic dreams. Alternately, Morpheus (who excels in presenting human images), Phobetor/Icelos (who presents images of beasts, birds and serpents), and Phantasos (who presents images of inanimate objects in prophetic dreams, such as earth, rock, water and wood).

In Homer's Iliad, an Oneiros is pictured as summoned by Zeus, receiving from him spoken instructions, and then going to the camp of the Achaeans and entering the tent of Agamemnon to urge him to warfare

The Odyssey speaks of the land of dreams as past the streams of Oceanus, close to where the spirits of the dead are led (Hades). Statiuspictures the Dreams as attending on slumbering Hypnos (Somnus in Latin) in a cave in that region.

In another passage of the Odyssey, dreams (not personified) are spoken of, by a double play on words, as coming through a gate of horn if true (a play on the Greek words for "horn" and "fulfil") or a gate of ivory if false (a play on the Greek words for "ivory" and "deceive"). For this image and its echoes in later literature, see Gates of horn and ivory.