Mithra is an ancient Indo-Iranian god of covenant, the sworn oath, truth and the light of the sun, honoured in Zoroastrianism as one of the greatest yazatas and the guardian of the given word, from whom no lie is hidden. The Avestan hymn to him, the Mihr Yasht, is one of the longest and finest in the Avesta, praising him as a warrior of a thousand ears and ten thousand eyes who ranges the lands watching over contracts and striking down those who break faith. His name is the same word as the Vedic Mitra, and the pairing of the two across the Indian and Iranian traditions is one of the strongest pieces of evidence for a shared Indo-Iranian religion before the two peoples separated. His feast, the Mihragan, remains a Zoroastrian festival.
Mithra's name and Persian associations fed into the very different Roman mystery cult of Mithras, wildly popular among soldiers and merchants of the Roman Empire from around the first to the fourth century CE, whose underground temples, mithraea, are found across the empire from Britain to Syria; but scholars of religion now generally treat Roman Mithraism as a distinct Greco-Roman mystery religion that borrowed the Persian god's name and prestige rather than a straightforward continuation of Zoroastrian Mithra worship, since core Roman Mithraic imagery, above all the tauroctony scene of Mithras slaying a bull, has no clear counterpart in the Avestan hymns to Mithra and no agreed origin within Zoroastrian tradition itself. The relationship between the two cults remains a genuinely debated question in the history of religion rather than a settled continuity.