The Greek Gods Family Tree, as Hesiod Tells It

Hesiod's Theogony, a Greek poem from around 700 BC, sets out the family of the gods in order, from the first powers to the children of Zeus. Below, the families come in the order Hesiod gives them, in Hugh G. Evelyn-White's 1914 translation, with the line numbers where each birth is told. Evelyn-White puts some names into English: Earth is Gaia, Heaven is Uranus, Night is Nyx. Here the English name comes first, as in the translation, with the Greek one beside it.

The first powers

Before anything has parents, four powers simply come to be: Chaos, Earth, Tartarus in the depths, and Eros. Chaos then gives rise to darkness and night, and Earth, alone, brings forth the sky that will become her husband.

Earth and Heaven: the Titans, the Cyclopes and the Hundred-Handed

Earth's union with Heaven produces three kinds of children. Twelve are the Titans, with Cronos the youngest. Three are the one-eyed Cyclopes, who later give Zeus his thunder. The last three have a hundred arms and fifty heads each, and Heaven hates them from the start.

“But afterwards she lay with Heaven and bare deep-swirling Oceanus, Coeus and Crius and Hyperion and Iapetus, Theia and Rhea, Themis and Mnemosyne and gold-crowned Phoebe and lovely Tethys. After them was born Cronos the wily, youngest and most terrible of her children, and he hated his lusty sire.”
Lines 116-138

Born from Heaven's wound

Heaven hides his children inside Earth, so she makes a sickle and Cronos maims his father with it. Even this act is a birth: the drops of blood that fall on Earth become the Erinyes, the Giants and the nymphs called Meliae, and from the foam where the severed flesh falls into the sea rises Aphrodite.

“and a white foam spread around them from the immortal flesh, and in it there grew a maiden.”
Lines 176-206

The children of the Titans

The Titans pair off, mostly with one another, and their children fill the world: the sun, moon and dawn, the rivers, the Olympian gods themselves, and the family of Prometheus. The most important couple is Cronos and Rhea, whose children Cronos swallows one by one until Rhea saves Zeus.

“But Rhea was subject in love to Cronos and bare splendid children, Hestia, Demeter, and gold-shod Hera and strong Hades, pitiless in heart, who dwells under the earth, and the loud-crashing Earth-Shaker, and wise Zeus, father of gods and men, by whose thunder the wide earth is shaken.”
Lines 453-491

Zeus and his wives

Once Zeus rules, the poem lists his unions in order. His first wife, Metis, he swallows while she is pregnant, and he gives birth to Athena himself, from his head. Hera, his last wife, bears Hephaestus alone, without him. Hermes, Dionysus and Heracles come after the list.

“Now Zeus, king of the gods, made Metis his wife first, and she was wisest among gods and mortal men.”
Lines 886-900

Cousins and grandchildren

A few more lines close the family of the great gods: Hecate, whom Zeus honours above all, is a granddaughter of the Titans; Poseidon's son rules the depths of the sea; and Aphrodite bears Ares three children, two of them the terrors of the battlefield.

Where later myths differ

Hesiod's family is not the only one the Greeks told. Other poets gave some gods different parents, and the best known case is Aphrodite: in Homer she is a daughter of Zeus and Dione, not of Heaven and the sea. When two sources disagree, this tree follows Hesiod. For the story that connects these births, the wars between the generations and the rise of Zeus, read Hesiod's Theogony, part by part.

Questions

Who is the oldest Greek god?

In Hesiod's Theogony, Chaos comes into being first. Earth (Gaia), Tartarus and Eros follow, and every other god descends from them.

Who were the parents of the Titans?

Earth and Heaven, the goddess Gaia and the god Uranus. They had twelve Titans, the three Cyclopes and three sons with a hundred arms each.

Who are the children of Cronos and Rhea?

Hestia, Demeter, Hera, Hades, Poseidon and Zeus. Cronos swallowed each of them at birth except Zeus, who was hidden in Crete.

Who is Aphrodite's father in the Theogony?

Hesiod has her grow from the sea foam around the severed members of Heaven (Uranus), so Heaven is her only parent. Homer tells it differently and makes her a daughter of Zeus and Dione.

How was Athena born?

Zeus swallowed his first wife, Metis, while she was carrying Athena, and later gave birth to Athena himself, from his own head.