Iliad 14 contains a negotiation between a queen and a contractor, and it is one of the funniest passages in the poem.
Hera needs Zeus asleep so that the Greeks can push the Trojans back. She goes to Hypnos on Lemnos and asks. He refuses flatly, and explains why: the last time he did this for her — during Heracles' return from Troy, when she raised a storm and blew the hero off course — Zeus woke up in a fury, scattered the gods about the palace looking for him, and would have thrown him out of the sky into the sea if Nyx, his mother, had not sheltered him. Zeus, Homer says, held off out of fear of doing something displeasing to swift Night.
Hera offers a golden throne made by Hephaestus with a footstool. He declines. She then offers one of the younger Graces, Pasithea, whom he has wanted all his life. He accepts — and insists she swear by the Styx, with one hand on the earth and one on the sea, naming the underworld gods as witnesses, because he is not doing this on a handshake.
He then perches in a fir tree on Mount Ida in the form of a bird and waits.
Where he lives
Ovid gives the fullest description of the house of Sleep, in Metamorphoses 11, and it is one of the best pieces of atmospheric writing in Latin poetry: a cave among the Cimmerians where the sun never reaches, no cockerel crows, no dog barks, no branch stirs, no human voice sounds, and the only noise is the river Lethe trickling over pebbles. Poppies and countless herbs grow at the entrance. There is no door, because a hinge might creak. In the middle stands an ebony bed with dark curtains, on which the god lies among his numberless sons, the Dreams.
Hesiod's version is starker: Sleep and Death live in the same house at the edge of the world, near the halls of Night, and the sun never looks on them with his rays. Sleep goes over the earth and the sea's broad back and is gentle to men; Death has a heart of iron.
The dreams
His children are the Oneiroi, and Ovid names three, giving each a specialty. Morpheus imitates human beings — gait, voice, expression, clothing — and is sent when a dream must appear as a specific person. Icelos, called Phobetor by mortals, becomes beasts, birds and serpents. Phantasos becomes earth, rock, water, wood and everything without life.
Morpheus is Ovid's invention or at least his naming, and he has had a career vastly out of proportion to his ancient footprint: he supplies "in the arms of Morpheus", and gave his name to morphine, isolated around 1804 by Friedrich Sertürner and named for the dream-bringer.
Homer's dreams are cruder and more sinister. In Iliad 2 Zeus deliberately sends a destructive Dream to Agamemnon in the shape of Nestor, telling him he can take Troy that day. The dream is a lie, sent to cause casualties. Greek epic does not treat dreams as messages from the unconscious; it treats them as visitors who may be working for someone.
The Odyssey gives the other famous image: Penelope's account of the two gates through which dreams come, one of horn and one of ivory. Those that pass through the sawn ivory deceive; those through the polished horn bring true things. The pun is on Greek words for ivory and deceive, horn and fulfil, and it survives in translation only as a description.
Sleeping as a religious act
Hypnos is not a god with temples, but sleep itself was a technical religious procedure. Incubation — sleeping in a sanctuary to receive a healing dream — was the entire operating method of the Asclepius sanctuaries, and Pausanias records that at Asclepius' shrine at Sicyon there was a relief of Sleep lulling a lion. At the oracle of the hero Amphiaraus at Oropos, the enquirer sacrificed a ram, spread its skin on the ground and slept on it; at the terrifying oracle of Trophonius at Lebadeia, described by Pausanias in unusual detail, the consultant descended into a chasm and returned in a state from which he had to be recovered and interviewed by priests.
So the god has little cult and the practice is everywhere, which is a distinction worth keeping. Greeks did not pray to Sleep; they used sleep to reach other powers.
Somnus, and the long visual tradition
The Roman Somnus is Ovid's version, and it is Ovid's cave that fed European art and literature — Chaucer's Book of the Duchess borrows the house of Sleep almost directly, Spenser uses it, and it stands behind a large amount of subsequent poetry about insomnia and oblivion.
In classical art Hypnos appears as a winged youth, often with wings at the temples rather than the shoulders, sometimes pouring a liquid from a horn or holding a poppy stem. A bronze head of Hypnos in the British Museum, a Roman copy of a Hellenistic original, is the best-known single object; the temple-wings are so distinctive that they identify him instantly.
Hypnosis, and what the name did next
The medical use of his name is a nineteenth-century coinage. The Scottish surgeon James Braid introduced neurypnology and then hypnotism in the early 1840s, deliberately replacing Mesmer's "animal magnetism" with a Greek term implying a sleep-like state — and later concluded the sleep analogy was wrong and tried unsuccessfully to change the word to monoideism. The name stuck anyway, and hypnosis is now one of the most widely known Greek-derived terms in clinical use.
Beyond that his modern presence is mostly hypnotic, hypnagogic for the state between waking and sleeping, and the enduring literary furniture of the poppy, the cave and the arms of Morpheus. He almost never appears as a character in modern retellings, which is a loss, because his one substantial scene in Homer shows a minor god driving a hard bargain with the queen of heaven and getting exactly what he asked for.
Morpheus, Pasithea, and the poppy
Is Morpheus the god of dreams?
He is one of the dream-shapers and specifically the one who takes human form, according to Ovid, who appears to be the first source to name him. The general term for dream-spirits is the Oneiroi, whom Hesiod makes children of Night directly rather than of Sleep. So "god of dreams" as a single office is a later tidying-up of a plural and vague group, and Morpheus' modern prominence comes largely from the drug and from twentieth-century fiction.
What is Pasithea?
One of the Graces, promised to Hypnos by Hera in the Iliad and named there as his desire. Later sources treat her as his wife and as a goddess of relaxation or hallucination. She is a good example of a figure who exists almost entirely as a term in someone else's bargain.
Do Greek sources treat dreams as meaningful?
Yes, but as communications rather than as self-expression. Dreams are sent, by gods, by the dead, or by other agents, and the interpretive question is who sent it and whether they are lying. Artemidorus' Oneirocritica, from the second century CE, is a full professional handbook of dream interpretation and is the ancient world's most substantial surviving text on the subject — closer to a reference manual than to anything psychological.
Why the poppy?
The opium poppy was cultivated in the Mediterranean from the Bronze Age and its sedative properties were well known; Greek medical writers discuss it, and poppy capsules appear in the iconography of Demeter as well as of Sleep. The plant's association with both sleep and grain-fields is why it turns up in the imagery of two quite different deities, and why the pharmacological line running from the poppy to Morpheus' name is not a coincidence but a continuity.