Helios saw Hades abducting Persephone. Demeter didn't think to ask him about her missing daughter, but wandered the earth morosely for months until her friend, the witchcraft goddess Hekate suggested that Helios might have been an eye witness.
Venus and Mars Caught in a Net Story
Helios owed Hephaestus for the cup that carries him to his morning daily starting point, which the smithy god had made for him, so when he witnessed an event of importance to Hephaestus, he didn't keep it to himself. He hurried to reveal the affair between Hephaestus' wife Aphrodite and Ares.
Parentage and Family
Although Hyperion may simply be part of Helios' name, usually Helios' parents are the Titans Hyperion and Theia; his sisters are Selene and Eos. Helios married the daughter of Oceanus and Tethys, Perseis or Perse, by whom he had Aeetes, Circe, and Pasiphae. By the Oceanid Clymene, Helios had a son Phaethon and maybe Augeas, and 3 daughters, Aegiale, Aegle, and Aetheria. These 3 daughters and two Helios had by Neaera, Lampetie and Phaethusa, were known as the Heliades.
Sun God: Helios to Apollo
Source: Oskar Seyffert (1894) A Dictionary of Classical Antiquities