Ahura Mazda, the name means the Wise Lord, is the supreme God of Zoroastrianism: uncreated, all-knowing, and entirely good. He is the creator of the ordered cosmos and of everything beneficent within it: light, life, truth, the good mind. In the Gathas, the ancient hymns attributed to the prophet Zarathustra, Ahura Mazda is the one addressed and praised, the origin of asha, the truth and right order that runs through the world, and the only being truly worthy of worship.
What sets Zoroastrian theology apart is what it does with evil. Ahura Mazda is not its author; suffering, falsehood and disorder come from a separate hostile spirit opposed to him. The good God creates and upholds the world through the Amesha Spentas, the Bounteous Immortals who are his agents and aspects. Zoroastrianism is therefore centred on one good God, while explaining evil through the cosmic conflict rather than laying it at that God's door.