Helios is the Greek god of the sun. Many people get him confused with Apollo because both are associated with light and the sun. But in Greek mythology, Helios is actually the god of the sun and in some cases he is the sun.
Helios is normally shown with the rays of the sun around his head in a kind of halo. He is also depicted with horses, even when he isn’t in his chariot. He is considered a younger god in physical appearance, beardless, and muscular. But the image of Helios is most often as above, with him riding in the chariot pulled by four white horses (which aren’t always winged).
The son of Hyperion and Theia, Helios took up with the Oceanid Perse. Their children were Aeetes (father of Medea), Circe (the sorceress from The Odyssey), and Pasiphae (mother of the Minotaur and Ariadne). With other women Helios fathered Phaethusa, Lampetia, and Phaeton.
Helios has no direct myths of him, but rather appears in the mythologies of his children. The most well-known tale involving Helios is that of his son Phaeton. Phaeton was the son of the nymph Clymene, but he didn’t know his father. When he asked his mother to tell him his father, he at first didn’t believe her when she told him it was the sun god himself who fathered him. When she told him to go in search of Helios and ask the truth, he did so, and traveled to the palace of the Sun in the east.
Phaeton approached his father and explained what brought him there. Helios confirmed Phaeton’s paternity and granted him a boon as proof and to allay Phaeton’s last doubts. Helios allowed Phaeton to ask for anything he wanted, and he swore an unbreakable vow for a god. When Phaeton asked to drive the chariot for one day, Helios regretted his promise, for he could not take back his word yet he knew his son was asking for a dangerous and deadly thing. Helios begged Phaeton to change his mind, choose anything else, but Phaeton remained stubborn.
Finally Helios had to relent, his oath having been sworn. He led Phaeton to the chariot and put him in it. Dawn came and it was time for the Sun. Helios gave Phaeton instruction on the horses and the road, telling him not to go too high nor too low, and let him go. At first Phaeton managed to keep the horses in check. But as he neared the apex, he lost control, and couldn’t keep the horses in their proper line. He went too high, and scorched the gods’ abode, then went too low and set the world aflame. The Earth herself prevailed upon Zeus for aid. Zeus looked down and saw Phaeton driving instead of Helios. Unable to call rain and cloud because of the heat, Zeus instead struck Phaeton with a thunderbolt, and Phaeton fell to his death. Helios and Phaeton’s sisters, the Heliades, lamented for all their days.
For a more in depth version of the myth, see here: Sacred Texts.
Helios was also considered all-seeing, and so was called upon by witnesses.
The sun is a life-giver. It’s part of the (scientific) reason that life on this planet even exists. He is kind and wise, and loving to his family. He is also a god of balance by nature, as seen in the myth of Phaeton–too high kills the gods, too low kills the people. A balance of his power is necessary if life is to survive.
In the desert, the sun can kill. And even today the sun’s rays can be deadly in the way of skin cancers. Too much of a good thing can sometimes be deadly, and that, I think, is part of the sun’s dark side. If the sun were to go out, humanity would perish. But too much sun can be just as deadly. If Helios goes out of balance, and it could be argued that his hasty promise to Phaeton was Helios out of balance, then the world suffers.
Also see: Encyclopedia Mythica.