In Greek mythology

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

, Hypnos was the personification of sleep; the Roman

Roman mythology

Roman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...

 equivalent was known as Somnus. His twin was Thánatos

Thanatos

In Greek mythology, Thanatos was the daemon personification of death. He was a minor figure in Greek mythology, often referred to but rarely appearing in person...

 (Θάνατος, "death"); their mother was the primordial goddess Nyx

Nyx

In Greek mythology, Nyx was the primordial goddess of the night. A shadowy figure, Nyx stood at or near the beginning of creation, and was the mother of personified gods such as Hypnos and Thánatos...

 (Νύξ, "night"). His palace was a dark cave where the sun never shines. At the entrance were a number of poppies and other hypnogogic plants. His dwelling has no door or gate so that he might not be awakened by the creaking of hinges.

Hypnos' three sons or brothers represented things that occur in dreams (the Oneiroi

Oneiroi

In Greek mythology, the Oneiroi were, according to Hesiod, sons of Nyx , and were brothers of Hypnos , Thanatos , Geras and other beings, all produced via parthenogenesis...

).