Protogenos

The Protogenoi, also known as the primordial gods, are the first race of immortals to come into existence, the majority of whom were born directly from the void of Chaos. Unlike the Titans and the gods, the Protogenoi are essentially the universe itself, and therefore, cannot truly be killed.

Birth of the Protogenoi
Initially, all the matter in the cosmos drifted around in a gloomy, soupy mist called Chaos. It was the first of the Protogenoi, and eventually some of its matter collected to form the earth, which developed a personality that called herself Gaea. After a period of time, the sky appeared: a great dome above the earth that became Ouranos. He married Gaea, but more Protogenoi followed in suit.



Water pooled out of the mist of Chaos and formed the first seas on earth, that like his predecessors, developed a consciousness: Pontus. Finally, another dome emerged from Chaos. Unlike Ouranos, however, this was Tartarus, the Pit of Evil right beneath the earth itself. Both of them harbored feelings for Gaea, which made her relationship with Ouranos rather difficult.

Other Protogenoi also appeared, namely Nyx, daughter of Chaos and Tartarus, as well as Protogenos of Night. Without aid of a consort, she gave birth to Hemera, who ironically became the Protogenos of Day.

Second Giant War
Following the end of the Second Olympian War, Gaea stirred from her slumber and began raising the Gigantes from Tartarus to oppose the Olympian gods. Not only do several deceased beings return to life, but other Protogenoi actively begin to participate in the war.

The Argo II is attacked by the Ourae when it tries to cross the Apennine Mountains, as they are children of Gaea.

After falling into Tartarus, Percy Jackson and Annabeth Chase encounter Akhlys, Nyx, and finally the embodiment of Tartarus himself. Through the combined efforts of Iapetus and Damasen fighting him off, Percy and Annabeth escape from Tartarus.

Abilities
As they are the very components that make up the universe, the Protogenoi are notably more powerful than other immortals. They have complete control of the domain they represent, which can rival or even exceed that of gods who preside over them.

All Protogenoi appear to be capable of manifesting in physical form to interact with lesser beings. Ouranos was able to appear in the form of a "tall, buff guy with longish hair", but still retained physical traits native to his domain, such as his skin being "blue with cloudy patterns" during the day and and "dark with glimmering stars" during the night.

Weaknesses
Despite their great power, Protogenoi are still susceptible to being weakened to the point of dormancy. This is shown when Ouranos was ambushed by his sons and had his physical body cut to pieces by Kronos with the scythe. After the murder, Ouranos' essence was scattered and his physical form permanently destroyed, but he remains alive and immortal nonetheless.

Furthermore, if separated from their domain, Protogenoi are relatively less powerful than they would be if they were in their element. This was exploited by Jason Grace when he used his aerokinetic powers to severe Gaea's contact with the earth, ultimately leading to her defeat when she is blown up by Leo Valdez and a missile.

Notable Protogenoi

 * Chaos: Protogenos of the Void
 * Gaea: Protogenos of the Earth
 * Ouranos: Protogenos of the Sky
 * Pontus: Protogenos of the Sea
 * Tartarus: Protogenos of the Pit
 * Nyx: Protogenos of Night
 * Erebos: Protogenos of Darkness
 * Hemera: Protogenos of Day
 * Aither: Protogenos of Air
 * Akhlys: Protogenos of Misery and Poison
 * Ourae: Protogenoi of Mountains

Trivia

 * Gaea is the only Protogenos to be in all five books of The Heroes of Olympus series.
 * The majority of the Protogenoi (with the exception of Gaea) make an appearance in The House of Hades as antagonists. They are the Ourea, Akhlys, Nyx, and Tartarus.