Which ancient Greek god rules the sun?

Helios is the ancient Greek god of the Sun. More often than not, people viewed or portrayed Helios as a powerful chariot, making his flaming chariot (or shimmering horses) race from east to west across the sky every day.

At night, according to legend, Helios crossed back to the east, floating in a golden cup on the stream of the ocean, while the mythical river thought to surround the flat land.

Since Helios looked at the sky all day, people assumed that he saw and heard everything that happened in this area; thus, both gods and people called him as a witness to various events or oaths.