Hypnos

Hypnos is a minor Olympian god of sleep. He is the son of Nyx and Erebus. His Roman counterpart is Somnus. He has at least three sons at Camp Half-Blood: Clovis and two others. Hypnos is probably where the words 'hypnotism' and 'hypnosis' are derived from. Somnus is where the medical term for sleepwalking; somnambulism is derived from. Hypnos was very cheeky and mischievous as a child, by putting people to sleep at serious moments.

History
Long before the Trojan War, Hera was angry at Heracles and she had persuaded Hypnos to make Zeus sleep while she tormented the hero. When Zeus awoke, he was in a rage. He searched for Hypnos and finally found him hiding in the arms of his mother, Nyx. Zeus overcame his anger and simply warned Hypnos not to try such a trick again and Hypnos went unpunished.

During the Trojan War, Hera wanted to distract Zeus from the battle so she could assist the Akhaians, who seemed to be losing the war. She wanted Hypnos to cast a spell of sleep on Zeus but he refused. At first Hera offered Hypnos a golden throne crafted by Hephaestus, but she was forced to raise the price when Hypnos reminded her of the only time he had dared cast sleep on Zeus.

In preparation for this new deception, Hypnos made Hera swear oaths of her sincerity. He agreed to help her deceive Zeus for the hand of Aglia, one of the Graces. He turned himself into a bird and, before Zeus could see him, hid in the tops of the trees on Mount Ida. He stayed hidden until Hera had seduced Zeus. When the father of gods was dulled by pleasure and sleep, Hypnos flew to Poseidon and urged him to increase his efforts in helping the Akhaians because Zeus was asleep and unaware of his meddling. Poseidon strode through the ranks of soldiers and urged them on. Finally, his bellowing and screeching roused Zeus from his slumber but, in that short time, the Akhaians had turned the battle back on the Trojans. Hera’s trick had worked. Zeus never found out that Hypnos had betrayed him.

His palace was a dark cave where sun never shines and river Lethe flowed beside it. Although Hypnos wasn't one of the most active gods of that time still he was famous for his role he played in the story of Endymion and Selene, the former goddess of moon. When, Endymion was sentenced eternal sleep by Zeus, he received the power to sleep with his eyes open by Hypnos so he could constantly watch his beloved Selene and because Hypnos himself was in love with the girl.

The Last Olympian
A cabin is built at Camp Half-Blood for Hypnos's children probably after he received his own throne on Olympus when the Battle of Manhattan ended. He gets his own throne after Percy makes all the Olympian gods and goddesses vow to an oath to the River Styx that they should honor the minor gods and goddesses and claim their demigod children when their children reach the age of thirteen just so that no other unclaimed demigod gets frustrated with the gods and decide to cause another war such as the Second Olympian War that ended with Luke's sacrificial death so that Kronos, Titan Lord of Time and possessor of his body, could not end up destroying Mount Olympus and that Olympus could survive.

The Lost Hero
Annabeth takes Jason, son of Zeus's Roman counterpart, Jupiter, to Hypnos' cabin at Camp Half-Blood when she realizes that Jason's memories are lost from his mind and that Clovis, Hypnos' demigod son, has the solution to why his memories are lost. There, Jason feels that he is starting to fall asleep and Annabeth tells him that even though Hypnos is the minor Olympian God of Sleep, even the inside of his cabin makes everyone feel like falling asleep then Annabeth said "The Hypnos cabin is even more dangerous than the Ares cabin at least in the Ares cabin you can learn where the land mines are". Annabeth says that Jason almost faded, although he doesn't know if she meant literally. Once Clovis hears Annabeth explain Jason's problem of lost memories, Clovis instantly awakens further and hears the story again. Clovis loves his pillow and hates being away from it.

Personality
Hypnos is said to do nothing much but sleep. He didn't play a role in the last Titan War.

Somnus
The Roman form of Hypnos is known as Somnus. While Hypnos is the god of sleep and didn't do much in Greek mythology, Clovis (a son of Hypnos) explains that Somnus would kill people that fell asleep at their posts, such as Palinurus; the helmsman of Aeneas, a Trojan hero. Clovis uses his father as an example of how the Roman and Greek gods, while still the same could be very different from each other.

Trivia

 * Somnolence, which is a state of near-sleep or desire for sleep, is named after his Roman counterpart Somnus. Also, somnabulation means sleepwalking (ambulabat means having walked in Latin)
 * Disorders like hypersomnia and insomnia are named after his Roman counterpart Somnus.