Hypnos

In Greek mythology, Hypnos (Greek: Ὑπνος, "sleep") was the winged god of sleep. He was a son of Nyx and the twin brother of Thanatos, the god of death. Sometimes, Erebus was given as his father. Hypnos was married to Pasithea, the goddess of relaxation and rest. He was the father of Morpheus, Phobetor, Phantasos, and the Oneiroi. Other sources list the Oneiroi as the brothers of Hypnos, rather than his children.

Hypnos lived in a cave in the Underworld with his brother from which the River Lethe flowed out of. Around the entrance to the cave, poppies grew due to Hypnos' association with poppies. Homer claims that Hypnos lived on the island Lemnos.

In Roman mythology, Hypnos was closely equated with Somnus.

Mythology
Hera once asked Hypnos if he could make Zeus fall asleep for a while so that she could wreak havoc upon the life of Heracles. Hera was angered at Heracles for attacking Troy so, after Zeus was asleep, she sent winds to blow his ship off course. After waking and realizing what Hera and Hypnos had done, Zeus chased after Hypnos. Hypnos fled to his mother, Nyx, and Zeus, not wanting to anger Nyx, held his anger at bay out of fear for the power of Nyx.

So, when Hera asked Hypnos to make Zeus fall asleep again, he was reluctant. However, Hera offered the hand of Pasithea in marriage. Hera lied to Aphrodite and got her to help Hera be irresistible to Zeus so when Hera and Zeus met on Mount Ida, Zeus was enamoured at her beauty. After making Zeus fall asleep, Hypnos went to Poseidon so that he could now help the Danaans and give them a victory. Zeus never found out about Hypnos' interaction in the victory of the Danaans.