Helios (ˈhiːli.ɒs/; Greek: Ἥλιος "Sun", Latinized as Helius) was the personification of the Sun in Greek mythology. Homer often calls him simply Titan or Hyperion, while Hesiod (Theogony 371) and the Homeric Hymn separate him as a son of the Titans Hyperion and Theia (Hesiod) or Euryphaessa (Homeric Hymn) and brother of the goddesses Selene, the moon, and Eos, the dawn. The names of these three were also the common Greek words for Sun, Moon and dawn. Ovid also calls him Titan, in fact "lumina Titan". The Emperor Julian the Apostate, forsook to show Romans that Helios was the only true god, and that the other Roman gods were just an image or manifestations of the supreme solar divinity, during that time the solar monotheism was the official religion of the Roman Empire, and Sol Invictus, was recognized as the supreme god.
Helios was imagined as a handsome god crowned with the shining aureole of the Sun, who drove the chariot of the sun across the sky each day to earth-circling Oceanus and through the world-ocean returned to the East at night. Homer described Helios's chariot as drawn by solar steeds (Iliad xvi.779); later Pindar described it as drawn by "fire-darting steeds" (Olympian Ode 7.71). Still later, the horses were given fiery names: Pyrois, Aeos, Aethon, and Phlegon.
As time passed, Helios was increasingly identified with the god of light, Apollo. However, in spite of their syncretism, they were also often viewed as two distinct gods (Helios was a Titan, whereas Apollo was an Olympian). The equivalent of Helios in Roman mythology was Sol, specifically Sol Invictus.