St. Cyril of Alexandria

Patriarch of Alexandria for thirty-two years, Cyril led the doctrinal battle against Nestorius and presided at the Council of Ephesus in 431, which defined Mary as Theotokos — God-bearer — and affirmed that the one Christ is true God and true man without division. His Christology shaped East and West.

Nephew of the patriarch Theophilus, Cyril inherited both his uncle's See and his combative temperament. He wrote voluminously — commentaries on the Pentateuch, Isaiah, and John, together with dense theological treatises — forging a vocabulary of incarnation that the Council of Chalcedon would refine but never discard.

His legacy is inseparable from the title he defended: if Mary is truly Theotokos, then the child she bore is one person, fully divine and fully human. Cyril died in 444, and the Church honors him as a Doctor whose fierce clarity preserved the mystery at the heart of the Christian faith.