I am now convinced this is Cyril of Alexandria. From Wikipedia: (c. 376 – 444) was the Patriarch of Alexandria from 412 to 444. He came to power when the city was at its height of influence and power within the Roman Empire. Cyril wrote extensively and was a leading protagonist in the Christological controversies of the later 4th and 5th centuries. He was a central figure in the First Council of Ephesus in 431, which led to the deposition of Nestorius as Patriarch of Constantinople.
Cyril is counted among the Church Fathers and the Doctors of the Church, and his reputation within the Christian world has resulted in his titles Pillar of Faith and Seal of all the Fathers, but Theodosius II, the Roman Emperor, condemned him for behaving like a "proud pharaoh", and the Nestorian bishops at the Council of Ephesus declared him a heretic, labelling him as a "monster, born and educated for the destruction of the church."