Zoroastrianism, also known as Mazdayasna and Behdin, is an Iranian religion. One of the world's oldest organized faiths, it is based on the teachings of the Avesta and the Iranian prophet Zoroaster. Zoroastrians exalt an uncreated and benevolent deity of wisdom, commonly referred to as "Ahura Mazda", as the universe's supreme being; opposed to Ahura Mazda is "Angra Mainyu", who is personified as a destructive spirit and the adversary of all things good. Zoroastranism combines a dualistic cosmology of good and evil with an eschatology predicting the ultimate triumph of Ahura Mazda over evil. Opinions vary among scholars as to whether Zoroastrianism is monotheistic, polytheistic, or henotheistic. Some assert that it combines elements of all three.

Dualism in cosmology or dualistic cosmology is the moral or spiritual belief that two fundamental concepts exist, which often oppose each other. It is an umbrella term that covers a diversity of views from various religions, including both traditional religions and scriptural religions.