Helios was born in the generation of the Titans, before the Olympian gods had won their throne, the child of Hyperion and Theia, two of the primordial deities who ruled the cosmos before Zeus's thunderbolt shook the heavens. Hyperion was the Titan of light, the one who watches from above, and Theia was the Titan of sight and the shining ether, the blue sky that holds the sun. Their three children were the lights of heaven: Eos, the dawn, who opens the gates of the east each morning with fingers of rose and saffron; Helios, the sun, who follows her across the day; and Selene, the moon, who takes the night when her brother has descended. The Homeric Hymn to Helios describes him as riding his golden-yoked chariot, piercingly gazing with his eyes from his golden helmet, bright rays beaming dazzlingly from him, his bright locks streaming from the temples of his head, a rich fine-spun garment glowing upon his body and fluttering in the wind, while stallions carry him across the heavens.

Each morning Helios rises from the palace of the sun, a golden dwelling that stands at the edge of the River Oceanus, the great stream that encircles the entire world. He emerges crowned with the aureole of the sun, a halo of blazing light, and climbs into his chariot, which was forged by Hephaestus, the divine smith whose limping gait and broken feet were the result of being thrown from heaven by Zeus. The chariot is drawn by four winged horses, sometimes called Pyrois, Eous, Aethon, and Phlegon, names that mean fire, dawn, burning, and flame. The Horae, the goddesses of the seasons, help him yoke the horses each dawn, and his sister Eos often rides beside him, opening the way. He drives across the dome of the sky from east to west, bringing light to mortals and gods alike, and when he reaches the land of the Hesperides in the far west, he descends into a golden cup or a golden bed that carries him through the northern streams of Oceanus back to his rising place in the east. In some accounts, he sails in a boat of gold by night; in others, he sleeps in a bed of gold beneath the earth. Either way, there is no rest for him or his horses, for the sun must rise again.

Helios sees everything. Because he travels across the entire sky each day, no deed on earth or in heaven is hidden from him. The gods invoke him as a witness when they swear solemn oaths, and mortals call upon his all-seeing eye when they make promises that must not be broken. In the Iliad, the goddess Hera swears by Helios and Earth and the gods of the underworld when she makes a false promise to Zeus, knowing that the sun will see through her deception. In the Odyssey, the nymph Calypso, the daughter of the Titan Atlas who held Odysseus captive on her island for seven years, swears by Helios and the gods when she promises to release him. The sun god's power of sight made him an invaluable witness in the myths of the gods. When Aphrodite, the goddess of love, lay with Ares, the god of war, in the bed of her husband Hephaestus, it was Helios who saw them from his chariot and told the smith, who then trapped the lovers in a net of unbreakable bronze and exposed them to the laughter of Olympus. When Persephone, the daughter of Demeter, the goddess of the harvest, was abducted by Hades, the gloomy king of the underworld, Helios was the only one who saw the deed and told the grieving mother where her daughter had gone.

Helios had many children by many lovers. With Perse, one of the Oceanid nymphs, the three thousand daughters of the primordial sea god Oceanus and his wife Tethys, he had three children who became the most famous of his offspring. Circe was the first, a witch of extraordinary power who lived on the island of Aeaea and turned Odysseus's men into swine with her magic before becoming his lover for a year. Aeëtes was the second, the king of Colchis at the eastern end of the Black Sea, who received the Golden Fleece from the fugitive prince Phrixus and hung it in a grove sacred to Ares, where a sleepless dragon stood guard until Jason and the Argonauts came to steal it. Pasiphaë was the third, the queen of Crete who married King Minos and, cursed by the gods with an unnatural passion for a white bull, gave birth to the Minotaur, the half-man half-bull monster that lurked in the Labyrinth of Knossos. With Clymene, another Oceanid nymph, Helios had a son named Phaethon and several daughters called the Heliades. With Rhode, a nymph of the island of Rhodes, he had seven sons who became the rulers of that island, so strong and wise that the three great cities of Rhodes, Ialysos, Kameiros, and Lindos, were named for three of them.

The most famous story of Helios is the tragedy of his son Phaethon. The boy grew up in the palace of his mother Clymene, proud and restless, and one day a companion mocked him for claiming divine parentage. Phaethon went east to his father's palace and begged Helios for proof that he was truly the son of the sun. Helios, moved by the boy's earnestness, swore a mighty oath by the River Styx, the boundary between the living world and the underworld, that he would grant his son any wish he desired. Phaethon asked to drive the sun chariot for a single day. Helios was horrified. He warned the boy that the horses were wild and fiery, that the path was narrow and dangerous, that the earth would burn if the chariot flew too low and freeze if it flew too high. But Phaethon would not be dissuaded, and Helios was bound by his oath. He placed the golden helmet on his son's head, crowned him with the seven rays of the sun, clothed him in the fiery robe, and gave him the reins.

Phaethon took the chariot at dawn, but the horses sensed a lighter hand upon the reins and bolted. They tore across the sky, now too high so that the earth froze and the constellations scorched, now too low so that the deserts of Libya were burned black and the rivers boiled away. The earth cried out to Zeus, the king of the gods, and Gaia, the primordial earth goddess herself, begged for deliverance. Zeus saw no other option. He hurled a thunderbolt from Olympus and struck Phaethon from the chariot, killing him instantly to save the world from destruction. The boy fell like a shooting star into the River Eridanus, and his sisters the Heliades mourned him so bitterly that the gods turned them into black poplar trees, their tears becoming amber as they wept upon the bank. Helios, heartbroken, refused to drive the chariot again, but the other gods begged him, and Zeus threatened him, and at last he resumed his duty, though he took his fury out upon his horses, whipping them for the death of his son. Some say he placed Phaethon among the stars as the constellation Auriga, the charioteer, so that the boy would be remembered forever in the heavens.

Helios played a crucial role in the voyage of Odysseus, the hero of the Trojan War whose cunning was legendary. On the island of Thrinacia, which some identify with Sicily, Helios kept seven herds of cattle and seven flocks of sheep, each numbering fifty head, immortal animals guarded by his daughters Lampetia and Phaethusa. The prophet Tiresias and the witch Circe, who was Helios's own daughter, both warned Odysseus to shun the island, but storms sent by Poseidon, the god of the sea, drove the ship there. Odysseus made his crew swear an oath not to touch the sacred animals, but after a month of contrary winds, the men were starving. While Odysseus was away praying, the crew leader Eurylochus convinced the others to slaughter the finest cattle and sacrifice them to the gods. When Odysseus returned, the meat was already roasting. Helios learned of the sacrilege from his daughters and was enraged. He went to Zeus and demanded vengeance, threatening to take the sun down to the underworld and shine it among the dead if he was not satisfied. Zeus promised to destroy the ship with a thunderbolt, and when Odysseus's crew put to sea again, the storm struck. The ship was shattered, every man drowned except Odysseus himself, who clung to the keel and was washed ashore on the island of Calypso, where he would remain for seven years.

Helios was worshipped most fervently on the island of Rhodes, where he was considered the patron deity from at least the early fifth century BCE. Legend said that Helios was the first to see the island emerge from the waters and claimed it as his own, and the island's name came from his nymph lover Rhodos. Every five years the Rhodians held the Halieia, Panhellenic games in his honour, and a chariot with four horses was thrown into the sea as an offering. The most famous monument to Helios was the Colossus of Rhodes, a gigantic bronze statue of the god that stood at the harbour mouth, one of the Seven Wonders of the Ancient World, until it was toppled by an earthquake in 226 BCE. In the rest of Greece, Helios was not a major cult deity, perhaps because the Greeks believed that barbarians built temples to the sun, but his name was invoked in serious oaths and Plato wrote that Socrates and others would greet and pray to the sun each day. Over time, the radiant god Apollo gradually absorbed Helios's role as sun god, and by the Hellenistic period the two were almost synonymous, though Helios never entirely disappeared from the Greek imagination.