Who is the Greek goddess of the dawn?

The Greek goddess of the dawn is Eos.

Eos was the divine personification of daybreak, imagined as rising each morning from the edge of Oceanus to scatter night and announce the Sun. In Greek poetry, she is especially famous by the Homeric epithet “rosy-fingered,” evoking the colors of the eastern sky. She was usually described as the daughter of the Titans Hyperion and Theia, and as the sister of Helios, the Sun, and Selene, the Moon.

Myths give Eos a chariot drawn by swift horses and connect her with the stars, the morning star Phosphorus, and the winds. Her best-known tragic romance involved Tithonus, a Trojan prince. She obtained immortality for him but failed to secure eternal youth, leaving him to grow endlessly old.

Eos is sometimes confused with Hemera, a related goddess of daylight, but the standard answer to the question about dawn is Eos. Her Roman counterpart is Aurora, and both names preserve the heritage of an older Indo-European dawn goddess.