Zoroastrianism or Zarathustraism (Mazdayasna in Farsi) is a religion founded in ancient Iran. It was created by the philosopher Zoroaster, also referred to as Zarathustra, and modeled after the pantheon of early Iranian gods. It teaches that there are two gods, one completely good (Ahura Mazda) and one completely evil (Ahriman). Probably originating in the early 2nd millennium BC, Zoroastrianism was the dominant religion in Arabia from 549 BC until the fall of the Sasanian empire in 7th century AD. Zoroastrianism was largely replaced by Islam in Arabia from 7th century onward. The religion is still practiced today, largely in Iran and also India (where refugees fled from persecution by the Muslims), but because of believers avoiding inter-marriage or converting outsiders, this limits the number of followers.
- "Zoroaster was thus the first to teach the doctrines of an individual judgment, Heaven and Hell, the future resurrection of the body, the general Last Judgment, and life everlasting for the reunited soul and body. These doctrines were to become familiar articles of faith to much of mankind, through borrowings by Judaism, Christianity and Islam; yet it is in Zoroastrianism itself that they have their fullest logical coherence [...]"
- Monotheistic belief in the god Ahura Mazda, who is almighty and good
- Ahura Mazda has an evil opponent called Aura Mainyu (which may have strongly influenced the idea of Satan in the Abrahamic religions).
- Existence is a cosmic battle between good and evil, and good will eventually triumph.
- "Now the two primal Spirits, who reveal themselves in vision as Twins, are the Better and the Bad, in thought and word and action. And between these two the wise ones chose aright, the foolish not so. And when these twain Spirits came together in the beginning, they created Life and Not-Life, and that at the last Worst Existence shall be to the followers of the Lie, but the Best Existence to him that follows Right."
- People have a choice (Free will) to be good or evil, or to choose truth or falsehood.
- Ahura Mazda has six aspects or emanations, known collectively as Amesha Spentas. These are considered to be the six most significant of the Yazata (angels), and are worthy of worship. (The concept is somewhat similar to the Christian trinity.)
- The nature of a person's afterlife depends on their actions in their Earthly life.
- The afterlife for the good will be the House of Song (Heaven). Evil people will go to the House of Wrong (Hell).
- Belief in Asha, which is a concept unique to this religion. It is sometimes compared to holiness, truth, order, righteousness or Dao.
- Domesticated animals, such as sheep, were generally viewed positively. The cow is sacred and the origin of all other animals. Animals have souls and good species should be protected and well treated. Dogs feature in later texts as a beneficent species. Dogs are required for some rituals and may be a substitute for a human in rituals requiring two people. Traditionally dogs must be fed before the first meal for the humans. Harsh punishments were specified for the mistreatment of beneficent animals. Strangely, Zoroastrians in some regions (and eras) practice animal sacrifice of domesticated animals.
- Reptiles, amphibians, felines and larger insects were considered evil and were systematically killed, although attitudes have move towards live-and-let-live in recent centuries. Domestic cats were traditionally viewed negatively.
- Zoroaster was born of a virgin.
- Prophesied the return of a Saoshynt or savior.
- Anyone is free to join the religion.
- Angels, known as Yazatas, which are mostly the other Persian deities reduced to a secondary rank, including Mithra. In contrast, demons help Ahura Mazda.
Their creed reads in part:
- "I declare myself a Mazda-worshipper [wisdom-worshipper], a supporter of Zarathushtra, hostile to the Daevas [wrong gods], fond of Ahura's [God's] teaching, a praiser of the Amesha Spentas [aspects or emanations of God], a worshipper of the Amesha Spentas. I ascribe all good to Ahura Mazda [wise God], 'and all the best,' Asha-endowed, splendid, xwarena-endowed, whose is the cow [a sacred animal], whose is Asha, whose is the light, 'may whose blissful areas be filled with light'.[...] I profess myself a Mazda-worshipper, a Zoroastrian, having vowed it and professed it. I pledge myself to the well-thought thought, I pledge myself to the well-spoken word, I pledge myself to the well-done action."
The Avesta is the primary holy text of Zoroastrianism. The major divisions of the surviving text are:
- Yasna (which include the Gathas or hymns, which are considered the most sacred part and believed to written by Zoroaster himself)
- Khorda Avesta
- "May Sraosha (Obedience) conquer disobedience within this house, and may peace triumph over discord here, and generous giving over avarice, reverence over contempt, speech with truthful words over lying utterance. May the Righteous Order gain the victory over the Demon of the Lie."
- "Holiness (Asha) is the best of all good: it is also happiness. Happy the man who is holy with perfect holiness!"
Curiously, the Khorda Avesta specifies a prayer to be recited before and after "the call of nature".
- "To live in fear and falsehood is worse than death."
The Denkard is a 9th century CE compendium of Zoroastrianism.
- "A thousand people cannot convince one by words to the extent that one person can convince a thousand by action."
- Prayer five times a day, in front of a sacred fire (called Atar) which represents a spiritual or mental fire, the presence of God and his Asha.
- Children go through an initiation ceremony called Sadreh-pushi.
- Marriages are called Govah-giri. Believers are encouraged to marry within the religion.
- The Farvahar is one of the main symbols of the religion, representing good thoughts, good words, good deeds. It was later adopted as a symbol of Iranian nationalism.
- Zoroastrians have seven annual festivals known as the Gahambars. Sadeh, Nowruz (the Persian new year or spring equinox), Tirgan, Jashan and Mehregan are among the main festivals.
- Various purification rituals, including the use of bull's urine as a disinfectant (which was a common ancient disinfectant).
- A Zoroastrian place of worship is called a fire temple, which keeps a sacred wood fueled fire burning. There are only 100-200 throughout the world, primarily in India. Offerings are usually placed on the fire by a priest while wearing a cloth mask to prevent impurity.
- Priests in Zoroastrianism are called mobeds, who primarily tend the sacred fires.
Exposure of the dead
Because the religion considers the dead to be ritually unclean, the traditional means of disposing of a body is exposure to the sun and scavenger birds for excarnation. The bodies are often placed in a special building, referred to as a Dakhma or in modern times as a tower of silence. This tradition is now dormant except in Mumbai. The sharp decline in vulture numbers has brought this practice into question with bodies taking up to a year to be consumed. 
Zoroaster is not reported in other historical documents apart from scripture, which is not surprising given that he probably lived in prehistorical times (that is before any surviving historical record). He is therefore a mythological figure.
Christian apologists argue for a much later date for Zoroaster's life of around 500-600 BCE, rather than the more usual 2000-1000 BCE, and then claim he actually borrowed his ideas from Judaism. The later date is based on the character Vishtaspa mentioned in the Avesta is the Vishtaspa, father of Darius I. In all probability, Darius's father was really named in honor of the earlier religious figure.
Inspired by the mythological Zarathustra, Friedrich Nietzsche used him as a model for the protagonist of his philosophical book Thus Spake Zarathustra. Nietzsche selected this religious figure because of his great influence and because he taught the virtues of morality and truthfulness. Nietzsche's character imagines Zarathustra revising his teaching by rejecting morality but retaining truthfulness:
- "Zarathustra was the first to see in the struggle between good and evil the essential cycle in the working of things. The translation of morality into the realm of metaphysics, as force, cause, as end in itself, is his work. But the very question presents its own answer. Zarathustra created this most fateful of all errors—morality; therefore he must be the first to recognize it."
Nietzsche's character is not considered part of the religion.