Gregory of Nazianzus (c. 329 - 390); also known as Gregory the Theologian or Gregory Nazianzen); 4th-century Archbishop of Constantinople. Gregory of Nazianzus is widely considered the most accomplished rhetorical stylist of the Patristic Age.

As a classically trained speaker and philosopher he infused Hellenism into the early church; establishing the paradigm of Byzantine theologians and church officials. Gregory made a significant impact on the shape of Trinitarian theology among both Greek- and Latin-speaking theologians; and he is remembered as the 'Trinitarian Theologian'. Much of his theological work continues to influence modern theologians; especially in regard to the relationship among the three Persons of the Trinity.

Along with the two brothers; Basil the Great and Gregory of Nyssa; he is known as one of the Cappadocian Fathers. Gregory is a saint in both Eastern and Western Christianity. In the Roman Catholic Church he is numbered among the Doctors of the Church; in Eastern Orthodoxy and the Eastern Catholic Churches he is revered as one of the Three Holy Hierarchs; along with Basil the Great and John Chrysostom.