Which patriarch of Alexandria defended the title 'Mother of God' at the Council of Ephesus in 431?

The patriarch of Alexandria who defended the title “Mother of God” at the Council of Ephesus in 431 was Saint Cyril of Alexandria.

The dispute centered on the Greek title Theotokos, meaning “God-bearer” or “Mother of God,” applied to Mary. Nestorius, patriarch of Constantinople, preferred Christotokos, “Christ-bearer,” because he wanted to emphasize the distinction between Christ’s divine and human natures. Cyril argued that refusing Theotokos could imply that Christ was divided into separate persons.

Cyril presided over the council, which opened at Ephesus on 22 June 431 before the arrival of John of Antioch’s delegation. The assembly condemned Nestorius and affirmed Mary as Theotokos, making the title a major expression of orthodox Christology. The council’s decision was later accepted by Emperor Theodosius II after considerable political confusion.

A common mix-up is attributing the defense to a later Marian theologian or to Athanasius. Athanasius strongly shaped fourth-century Christology, but Cyril was the Alexandrian patriarch who led the specific Ephesus controversy.