Zoroaster, Ζωροάστρης (Ζαθραύστης, Ζαράτας), is the Greek form Old Iranian Zarathuštra. He is considered by Zoroastrian tradition as prophet of a new religion; the revolutionary nature of his teachings is, however, debatable. In the oldest part of the Avesta, the Gāthā, he is called a ma̢thrān, ‘he who possesses the sacred formulas’. The Gāthā, ritualistic hymns, portray a dualistic system in which Aṣ̌a (truth, rightness) is opposed to Druj (lie, deceit) with *Ahura Mazdā is the supreme deity. They are dated, on linguistic grounds, to c.1000 bce. Whether Zoroaster was a historical figure, lived around this date, and wrote the Gāthā is debated; his persona certainly served as focal point of an emergent religious community. A date in the 6th cent. bce is suggested by late Zoroastrian tradition, but not supported by conclusive historical evidence. The Greeks knew of Zoroaster by the 5th cent. bce (*Xanthus(2) of Lydia in Diog.