Nestorius (b. after 351; d. after 451 CE), Patriarch of Constantinople and heresiarch. He gave his name to the doctrine (Nestorianism) that there were two separate Persons in the Incarnate Christ, the one Divine and the other human (as opposed to the orthodox teaching that in the Incarnate Christ was a single Person, at once God and man); whether Nestorius taught this is disputed.
In 428 Theodosius II invited Nestorius, then a monk, to become Patriarch of Constantinople. When Nestorius’ chaplain preached against the use of the term ‘Theotokos’ as savouring of heresy (Apollinarianism), he supported him. Controversy developed around the propriety of the term. At a Council in Rome in 430 Pope Celestine I condemned Nestorius’ teaching, and Cyril of Alexandria was commissioned to pronounce sentence of deposition if he would not submit. Cyril delivered his sentence into Nestorius’ hands by legates sent to Constantinople, condemning Nestorius in a set of twelve anathemas and requiring him to retract within ten days. Meanwhile the Emperor had called a General Council; this met at Ephesus in 431 and deposed Nestorius (….). In 436 he was banished to Upper Egypt, where he died (date unknown).
Nestorius’ chief writings were letters and sermons which have mostly survived only in fragments. He also wrote a treatise known as the ‘Bazaar of Heracleides. This was written when the theological climate had changed; in it Nestorius claimed that his own beliefs were identical with those then being sustained by the orthodox (against the Eutychians). What he taught and how far it was heretical is unclear.
In the late 5th and 6th centuries, the term ‘Nestorian’ was applied by their opponents to all upholders of a strict Antiochene Christology; consequently the Church of the East came to be called ‘the Nestorian Church’.
Taken from: The Concise Oxford Dictionary of the Christian Church, Ed. Livingstone. Dr. E. A. 2006, entry “Nestorius” p. 405, pub. Oxford University Press.