Introduction
Mithra is a Yazata, one of the most important divine beings of Zoroastrianism below Ahura Mazda himself, associated with covenants, contracts, oaths, and light. His name is directly related to the Sanskrit Mitra, an Aditya of the Vedic pantheon, reflecting the shared Indo-Iranian religious ancestry of the two traditions before they diverged.
Note: this Mithra is a distinct figure from the Vedic and Hindu god Mitra, though the two names share a common origin.
Guardian of covenants
Mithra's central domain in Zoroastrian religion is the sanctity of the spoken word: contracts, oaths and covenants of every kind, from personal agreements to treaties between nations, fall under his protection, and breaking one's word was considered a serious offence against him.
Associations with light and the sun
Mithra is closely associated with light, and, in later tradition, increasingly identified with the sun itself, watching over the world from the sky and unable to be deceived, since nothing can be hidden from the light.
The Mihr Yasht
A long hymn dedicated to Mithra, the Mihr Yasht, is one of the most extensive and well-preserved texts of the Younger Avesta, describing his power, his chariot, and his role in punishing those who break covenants.
Roman Mithraism
Mithra's name and some elements of his cult spread far beyond Iran: the Roman mystery religion of Mithras, popular particularly among soldiers across the Roman Empire from roughly the first to fourth centuries CE, drew on his name and some Persian associations, though Roman Mithraism developed its own distinct mythology, iconography (notably the tauroctony, or bull-slaying scene) and ritual practice, substantially different from Zoroastrian Mithra worship.