The priestly caste is a social group responsible for officiating over sacrifices and leading prayers or other religious functions, particularly in nomadic and tribal societies.
In some cases, as with the Brahmins of India and the Kohanim and Levites of ancient Israel, the caste was a hereditary one, with a person's position as a priest depending on his biological descent. Zoroastrianism also has a hereditary priesthood, as does Alevism, Yezidism and Yarsanism. In Sufism, the spiritual guide is also often a hereditary leader, while the Sayyids of South Asia, who claim descent from the Islamic Prophet Muhammad, have been described as a priestly caste. The Archiereis responsible for the Roman imperial cult were often related and at least in the Greek East, there appear to have been even dynasties of high priests.