The Shining One of the Rigveda: husband of Saranyu, father of Yama, of the Ashvins and of Manu. The Yajurveda and Brahmanas call him an Aditya, and later his name is a common name of the sun.
Sources: Vedic Mythology, A. A. Macdonell (1897); Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer · see Vivasvat's web
Vivasvat is in the Taittiriya Brahmana's list of the eight sons of Aditi and is called Aditya in the Yajurveda and Brahmanas; the Puranas keep him among the twelve.