Originally, a patriarch was a man who exercised autocratic authority as a pater familias over an extended family. The system of such rule of families by senior males is termed patriarchy.
The word is derived from Greek πατριάρχης (patriarchēs), meaning "chief or father of a family", a compound of πατριά (patria), meaning "family", and ἄρχειν (archein), meaning "to rule"
Abraham, Isaac, and Jacob are referred to as the three patriarchs of the people of Israel, and the period during which they lived is termed the Patriarchal Age. The word patriarch originally acquired its religious meaning in the Septuagint version of the Bible.
Today, the word has acquired specific ecclesiastical meanings. In particular, the highest-ranking bishops in Eastern Orthodoxy, Oriental Orthodoxy, the Catholic Church (above major archbishop and primate), and the Church of the East are termed patriarchs (and in certain cases also popes). The office and the ecclesiastical circumscription of such a patriarch is termed a patriarchate. Historically, a patriarch has often been the logical choice to act as ethnarch of the community identified with his religious confession within a state or empire of a different creed (such as Christians within the Ottoman Empire).