Hypnos

Hypnos (Ancient Greek: Ὕπνος) is the personification of sleep and the twin brother of Thanatos the personification of death. Hypnos lives in Tartarus with his mother Nyx and his siblings such as the Oneiroi, the Fates, Thanatos, Hecate, Hemera and others. He lives in a cave in Tartarus right next to the river Lethe, the river of Forgetfulness.

Etymology
The name "Hypnos" was the literal word for sleep in ancient greek. The English word "hypnosis" is derived from his name, referring to the fact that when hypnotized, a person is put into a sleep-like state (hypnos "sleep" + -osis "condition"). Additionally, the English word "insomnia" comes from the name of his Latin counterpart, Somnus. (in- "not" + somnus "sleep"), Hypnos as well as a few less-common words such as "somnolent", meaning sleepy or tending to cause sleep. Consequently, the condition for someone who cannot or has difficulty falling asleep is "insomniac."

Family
Hypnos is a son of Nyx, primordial goddess of the night and Erebus, personification of darkness. Hypnos is the brother of Aether, Hemera, Thanatos, the Fates, the Keres, the Oneiroi, the Hesperides and many others. Hypnos is the husband of Pasithea, youngest of the Graces, daughters of Zeus and Eurynome. Ovid names him the father of the Oneiroi, gods of dreams.

Hypnos in mythology
Hypnos was depicted as a young man with wings on his shoulders or brow. His attributes included either a horn of sleep-inducing opium, a poppy-stem, a branch dripping water from the river Lethe (Forgetfulness), or an inverted torch.

His horn of sleep-inducing opium was used to lull both mortals and gods to sleep. Hypnos would then open two gates that the Oneiroi used to get through to the minds of people, causing them to dream. The Gate of Horn provided prophetic dreams, while The Gate of Ivory provided dreams that are misleading and deceptive. But the dreams each person would have depended on the individual.