Zoroastrianism is the ancient Iranian, pre-Islamic religion of the followers of the Persian prophet Zoroaster (c. 6th century BCE). Zoroaster, also known as Zarathustra, had visions of a wholly good creator God, Ahura Mazda - 19th century scholars called the tradition "Mazdaism" - who is opposed by the evil being Angra Mainyu. Much Zoroastrian theology is based on the dualism of good versus evil, as played out in the battle between Ahura Mazda and Angra Mainyu; Ahura Mazda will eventually prevail, and the cosmos will be renewed and all beings will reunite with Ahura Mazda. In Zoroastrianism there is little or no distinction between the physical and the spiritual realms, and thus there is a strong ethical component in the tradition because the personal struggle of good and evil in the human realm is believed to have cosmic ramifications. It is thus the responsibility of each believer to fight against evil on all fronts. The primary sacred text of Zoroastrianism is the Avesta ("Book of Law"), which includes hymns attributed to Zoroaster, instructions for festivals, rituals of purity, and spells against demons. Zoroastrianism was the official state religion of three successive empires in Iran from 550 BCE to 642 CE. During this period, Zoroastrianism had broad influence in what is now modern Pakistan, Afghanistan, Turkey, and Palestine. Although Zoroastrianism nearly disappeared after the emergence of Islam in the region, there are still small Zoroastrian communities scattered throughout the Middle East and India (where they are sometimes known as "Parsis").
Rohinton Rivetna explains what it means to be a Zoroastrian in today's world
God - Ahura Mazda and Angra Mainyu (dualism), and other deities