Ahura Mazda in the context of "Frashokereti"

Zoroastrianism, also called Mazdayasna or Behdin, is an Iranian religion centred on the Avesta and the teachings of Zarathushtra Spitama, who is more commonly referred to by the Greek translation, Zoroaster (Greek: Ζωροάστρις Zōroastris). Among the world's oldest organized faiths, its adherents exalt an uncreated, benevolent, and all-wise deity known as Ahura Mazda (𐬀𐬵𐬎𐬭𐬀⸱𐬨𐬀𐬰𐬛𐬁), who is hailed as the supreme being of the universe. Opposed to Ahura Mazda is Angra Mainyu (𐬀𐬢𐬭𐬀⸱𐬨𐬀𐬌𐬥𐬌𐬌𐬎), who is personified as a destructive spirit and the adversary of all things that are good. As such, the Zoroastrian religion combines a dualistic cosmology of good and evil with an eschatological outlook predicting the ultimate triumph of Ahura Mazda over evil. Opinions vary among scholars as to whether Zoroastrianism is monotheistic, polytheistic, henotheistic, or a combination of all three. Zoroastrianism shaped Iranian culture and history, while scholars differ on whether it significantly influenced ancient Western philosophy and the Abrahamic religions, or gradually reconciled with other religions and traditions, such as Christianity and Islam.

Originating from Zoroaster's reforms of the ancient Iranian religion, Zoroastrianism began during the Avestan period (possibly as early as the 2nd millennium BCE), but was first recorded in the mid-6th century BCE. For the following millennium, it was the official religion of successive Iranian polities, beginning with the Achaemenid Empire, which formalized and institutionalized many of its tenets and rituals, and ending with the Sasanian Empire, which revitalized the faith and standardized its teachings. In the 7th century CE, the rise of Islam and the ensuing Muslim conquest of Iran marked the beginning of the decline of Zoroastrianism. The persecution of Zoroastrians by the early Muslims in the nascent Rashidun Caliphate prompted much of the community to migrate to the Indian subcontinent, where they were granted asylum and became the progenitors of today's Parsis. Once numbering in the millions, the world's total Zoroastrian population is estimated to comprise between 110,000 and 120,000 people, with most of them residing either in India (50,000–60,000), in Iran (15,000–25,000), or in North America (22,000). The religion is thought to be declining due to restrictions on conversion, strict endogamy, and low birth rates.

Bactria (/ˈbæktriə/; Bactrian: βαχλο, Bakhlo), or Bactriana, was an ancient Iranian civilization in Central Asia, located in the area south of the Oxus River (modern Amu Darya) and north of the Hindu Kush mountains, within modern-day Afghanistan, Tajikistan and Uzbekistan. Bactria was strategically located south of Sogdia and west of the Pamir Mountains. These mountain ranges acted as "walls" protecting Bactria from three sides, with the Pamir mountains to the north and the Hindu Kush to the south forming a junction, and the Karakoram range towards the east.

Called "beautiful Bactria, crowned with flags" by the Avesta, the region is considered, in the Zoroastrian faith, to be one of the "sixteen perfect Iranian lands" that the supreme deity, Ahura Mazda, had created. It was once a small and independent kingdom struggling to survive against nomadic Turanians. One of the early centres of Zoroastrianism, and capital of the legendary Kayanian dynasty, Bactria is mentioned in the Behistun Inscription of Darius the Great as one of the satrapies of the Achaemenid Empire; it was a special satrapy, ruled by a crown prince or an intended heir. Bactria was the centre of Iranian resistance against the Greek Macedonian invaders after the fall of the Achaemenid Empire in the 4th century BC, but eventually fell to Alexander the Great.

Angra Mainyu (/ˈæŋrə ˈmaɪnjuː/; Avestan: 𐬀𐬢𐬭𐬀⸱𐬨𐬀𐬌𐬥𐬌𐬌𐬎, romanized: Aŋra Maniiu) is the Avestan name of Zoroastrianism's hypostasis of the "destructive/evil spirit" and the main adversary in Zoroastrianism either of the Spenta Mainyu, the "holy/creative spirits/mentality", or directly of Ahura Mazda, the highest deity of Zoroastrianism. The Middle Persian equivalent is Ahriman (/ˈɑːrɪmən/; Middle Persian: 𐭠𐭧𐭫𐭬𐭭𐭩, romanized: Ahreman). The name can appear in English-language works as Ahrimanes.

Ancient Iranian religions were a set of ancient beliefs and practices of the Iranian peoples before the rise of Zoroastrianism. The religion closest to it was the historical Vedic religion that was practiced during the Vedic period. The major deities worshipped were Ahura Mazda and Mithra from Iran to Rome, but Atar was also worshipped, as names of kings and common public showing devotion to these three exist in most cases. But some sects, the precursors of the Magi, also worshipped Ahura Mazda, the chief of the Ahuras. With the rise of Zoroaster and his new, reformatory religion, Ahura Mazda became the principal deity, while the Daevas were relegated to the background. Many of the attributes and commandments of Varuna, called Fahrana in Median times, were later attributed to Ahura Mazda by Zoroaster.

The Iranian peoples emerged as a separate branch of the Indo-Iranians in the 2nd millennium BC, during which they came to dominate the Eurasian Steppe and the Persian Plateau. Their religion is derived from Iranian religions, and therefore shares many similarities with the Vedic religion of India. Although the Persian peoples left little written or material evidence of their religious practices, their religion is possible to reconstruct from scant Iranian, Babylonian and Greek accounts, similarities with Vedic and other Indo-European religions, and material evidence.

The Behistun Inscription (also Bisotun, Bisitun or Bisutun; Persian: بیستون, Old Persian: Bagastana, meaning "the place of god") is a multilingual Achaemenid royal inscription and large rock relief on a cliff at Mount Behistun in the Kermanshah Province of Iran, near the city of Kermanshah in western Iran, established by Darius the Great (r. 522–486 BC). It was important to the decipherment of cuneiform, as it is the longest known trilingual cuneiform inscription, written in Old Persian, Elamite, and Babylonian (a variety of Akkadian).

Authored by Darius the Great sometime between his coronation as king of the Persian Empire in the summer of 522 BC and his death in autumn of 486 BC, the inscription begins with a brief autobiography of Darius, including his ancestry and lineage. Later in the inscription, Darius provides a lengthy sequence of events following the death of Cambyses II in which he fought nineteen battles in a period of one year (ending in December 521 BC) to put down multiple rebellions throughout the Persian Empire. The inscription states in detail that the rebellions were orchestrated by several impostors and their co-conspirators in various cities throughout the empire, each of whom falsely proclaimed himself king during the upheaval following Cambyses II's death. Darius the Great proclaimed himself victorious in all battles during the period of upheaval, attributing his success to the "grace of Ahura Mazda".

Arya (Avestan: 𐬀𐬌𐬭𐬌𐬌𐬀, airiia; Old Persian: 𐎠𐎼𐎡𐎹, ariyaʰ; Middle Persian: 𐭠𐭩𐭫‎, er; Parthian: 𐭀𐭓𐭉‎, ary; Bactrian: αρια, aria) was the ethnonym used by Iranians during the early History of Iran. In contrast to cognates of Arya used by the Vedic people and Iranic steppe nomads, the term is commonly translated using the modern ethnonym Iranian.

During Old Iranian times, the term was connected with one's lineage, with speaking an Iranian language and with the worship of Ahura Mazda. Being an Arya, therefore, had ethnic, linguistic and religious aspects. During the Middle Iranian period, it acquired a distinct political aspect through the concept of Eran Shahr (Aryas' dominion). Arya was also contrasted with Anarya (Avestan: 𐬀𐬥𐬀𐬌𐬭𐬌𐬌𐬀, anairiia; Middle Persian: 𐭠𐭭𐭩𐭥‎, aner), denoting non-Iranian lands and peoples.

Bagrevand (also spelled Bagrewand) was a region of Armenia.

The Old Iranian etymology of the name is disputed. It is either derived from *bāγa.raivanta ("rhubarb garden") or baga-raēvanta-, which either means "the rich giver" (Mithra) or "the bounteous God" (Ahura Mazda).