The Protogenoi: The earliest beings. These primeval gods were the first elements of the universe itself. They were personifications of various things; Air, Earth, Sea , Sky, Underworld, Darkness, Night, Light, Day, Procreation, Time.
The first to come into being was Chaos:
Not much detail is given to Khaos, as it was an empty void that simply appeared. Lifeless matter, with no form.It held all the elements within itself. From this, the Protogenoi came.
Some myths say that Chaos actually originated from the two Gods below: Anake and Khronos.Though Hesoid and Ovid disagree.
Ananke (Anance): Goddess of Inevitability, Compulsion and (more commonly known) Necessity.She neither came from Khaos or was born, rather she was self-made. She was shown as a serpent-like being who encompassed the universe within her arms. She is forever coiled around Khronos, her mate.
Khronos (Chronus): God of Time. Similar to Anake, he was self-formed. He is shown with a serpent-like body and three heads: a mans, a bulls, and a lions.He doubled as the Titan Kronos and was referred to as 'Father Time' or 'Eternal Time'.
Gaia (Gaea): Goddess of Earth. One of the very first. Known as 'Great Mother'. She bore children to Ouranos, Pontos, and Tartaros.In artwork she is shown as a motherly looking women, clothed in green,never able to leave her element. She is often shown attached to the Earth. In mythology she was the adversary of most other Gods. She fought with her husband Ouranos when he locked her sons away inside her. Then she fought her own son when he did the same, helping Zeus to fight him. Then she fought Zeus when he bound her Titan-borne sons in Tartaros.
Ouranos (Uranus): God of Sky. He was a personification of the sky and husband of Gaia. In art, he is not shown for some significant amount of time. Though in the Roman-era, he appeared behind Gaia with the zodiac wheel in his hand. Together with Gaia, he had twelve sons and six daughters. He locked his eldest, Kyklopes and Hekatonkheires, in the Earth because he was disgusted by their appearances. When Gaia had her sons rebel, four took their places at the corners of the world and held him down. The fifth took a sickle that was given to him by his mother and castrated Ouranos. His blood fell to Earth and made the Erinyes and Gigantes.
Eros: God of Love and Procreation. In Hesoid's version of the begining, he describes Eros as 'fairest among the deathless Gods'. Sometimes he was referred to as 'Phanes' and thought of as equal to 'Thesis' and 'Physis'. In pre-Homeric myth, he was the son of Aether and Hemera.
Appearance-wise, Eros is shown as a youthful boy with golden wings, usually carrying a bow and arrows that were gold-tipped.
Nyx: Goddess of Night. A firstborn elemental god, daughter of Chaos. She bore children to her brother, Erebus, and some of her own creation. Her children include Aether (Light), Hemera (Day), Moros (Doom), Thanatos (Death), Hypnos (Sleep), Charon, the Fates, Nemesis (Retribution), and Eris (Strife). Most of her other children were personifications of vague abstracts. Apate (Deceit), Geras (Old Age), the Keres (Dooms), Momos (Blame), Oizus (Misery),and Philotes (Tenderness). Nearly all of them dwelt in the underworld. She is either shown as simply night, or as a winged Goddess.
Erebos (Erebus): An elemental God of Darkness.Erebus was born along with Gaea, Eros and Nyx. He was both brother and consort to Nyx.He fathered Aether and Hemera. He was thought to be a personification of a specific region in the Underworld where the dead must pass, being near Tartarus. Hades was another name of his. His dark mist encompassed the edge of the world and filled the hallows of Earth.He is not shown in most art.
Tartarus: Personification of the deepest part of the Underworld.
Aither (Aether): Another elemental God. He was God of Upper Air (the heavens). Above him was Ouranos, and below passed his mother Nyx and his sister Hemera. Some mythology shows his counterpart as being Aithre, the Titanis of Clear Blue Sky. Aether is thought of as the highest of the airs, the air that the Gods themselves breathe. The middle being Chaos and the last being Erebus. Some say he was the father of Uranus.In Hesoid's Theogony, Aether acted as Zeus's defensive wall that locked Tartarus away from the rest of the Cosmos.He is called the 'Soul of the world'.
Hemera: Goddess of Day. Daughter of both Erebus and Nyx, and sister/wife of Aether. Hemera's job was to disperse night's mist and let light from the heavens shine down to Earth in order to bring morning.She was closely identified to Hera and Eos, though Hesiod describes her as more of a divine substance rather than a being. However, in Cicero's De Natura Deorum it is said that if Uranus is a God than Hemera must be as well.Mythology lists Thalassa as their child.
Pontus: Personification of the Sea. Son of Gaea. He fathered Nereus, Eurybia, Thaumas and Phorcys. He also fathered the sea beast, Ceto. His son was more prevalent in Mythology. It is said that his wife was Thalassa.
Nereus: A God of the Sea. He married Doris and bore the Nereids, which are fifty sea-nymphs. It is said that he is a shape-shifter and has prophetic powers.
Ourea: Primeval Gods, sometimes thought of as Spirits, of each mountain.
Okeanos (Oceanus): Titan God or the river Okeanos, which circled the entire Earth. His wife was Tethys. Together they formed the river gods and nymps of springs and fountains. He was less active than his brother, Titanes. He did not help castrate Ouranos and did not fight the young Olympian Gods. He is shown with bull horns atop his head, the lower half of his body being serpentine.
Nesoi: Primeval Gods of the islands. It is said that Poseidon broke them apart and cast them into the sea.
Cicero, De Natura Deorum