Gregory of Nazianzus (c. 329 – 25 January 390) was a 4th-century Archbishop of Constantinople, and theologian. He is widely considered the most accomplished rhetorical stylist of the patristic age.  As a classically trained orator and philosopher he infused Hellenism into the early church, establishing the paradigm of Byzantine theologians and church officials.  Saint Gregory was saint patron of medieval Bosnia before the Catholic conquest when he was replaced by Saint Gregory the Great.

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 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 Catholic Church he is numbered among the Doctors of the Church.

Source: https://en.wikipedia.org/wiki/Gregory_of_Nazianzus

St. Gregory Nazianzen - c. 372 A.D. Orations St. Gregory Nazianzen - c. 372 A.D. Letters