Short answers, pulled from the story.
Theia is a Titan in Greek mythology, the goddess of sight, regarded as the goddess from which all light proceeded. She is the daughter of Uranus and Gaia and, by her brother-husband Hyperion, the mother of Helios, Selene, and Eos.
Theia is a goddess of sight and brilliance, associated with glittering in particular and glory in general. A scholium on Pindar traces gold to her, since the Sun came from Theia and Hyperion, and from the Sun came gold.
Theia and Hyperion are the parents of Helios the Sun, Selene the Moon, and Eos the Dawn. Catullus called these three lights of the heavens "Theia's illustrious progeny" in the sixty-sixth of his carmina.
Theia is also called Thea, Thia, Euryphaessa, Aethra, and Basileia. The name Euryphaessa joins eurýs, meaning wide, with pháos, meaning light, while Basileia means queen in Diodorus's account.
The hypothetical planet Theia is named for the goddess because of her role as the mother of the Moon goddess Selene. Under the giant impact hypothesis, this planet collided with the Earth and created the Moon.
In Diodorus's account, Theia is identified as Basileia, the eldest daughter of king Uranus who reared her brothers and was called the Great Mother. After her brothers killed Hyperion and drowned Helios in the Eridanus river, Selene threw herself off the roof, and a frenzied Basileia wandered the land until the people raised altars to her.