Nestorius (c. 386 – c. 451) is Archbishop of Constantinople from April 10, 428 to August 431 (when the emperor Theodosius II confirms his condemnation by the Cyrillian faction at Ephesus on 22 June).

His teachings include a rejection of the long-used title of Theotokos ("Mother of God") for the Virgin Mary, and are understood by many to imply that he does not believe that Christ was truly God.

However, Nestorius actually is concerned that the "Theotokos" cult is dangerously close to venerating Mary as a goddess.

This brings him into conflict with other prominent churchmen of the time, most notably Cyril of Alexandria, who accuses him of heresy.

Nestorius sks to defend himself at the First Council of Ephesus in 431, but instead he finds himself formally condemned for heresy by a majority of the bishops and subsequently removed from his see.

On his own request, he retires to his former monastery in or near Antioch.

In 435, Theodosius II sends him into exile in Upper Egypt, where he lives on till 450 or 451, strenuously defending his orthodoxy.

His last major defender within the Roman Empire, Theodoret of Cyrrhus, finally agrees to anathematize him in 451 (during the Council of Chalcedon); from then on he has no defenders within the empire.

But the Church of the East (that is, the Church in eastern Mesopotamia and Persia, under Sassanian rule) never accepts his condemnation.

This leads later to western Christians giving the name the 'Nestorian Church' to the Church of the East (the modern Assyrian Church of the East), even though it never regarded him as an authoritative teacher.

The discovery and publication of his 'Book [or Bazaar] of Heraclides at the beginning of the 20th century led to a reassessment of his theology in western scholarship.

It is now generally agreed that his ideas were not far from those that eventually emerged as orthodox, but the orthodoxy of his formulation of the doctrine of Christ is still controversial.

This is due to the fact that the Second Council of Constantinople of 553 confirmed the validity of the condemnation of Nestorius, refuting the impious letter of Iba that affirms that Nestorius was condemned without the due inquiry.