Gregory Nazianzen, also known as Gregory of Nazianzus, was a prominent early Christian theologian and one of the Cappadocian Fathers. Born around 329 AD in what is now Turkey, he played a crucial role in the development of Christian doctrine, particularly concerning the nature of the Holy Trinity. His eloquent sermons and writings helped shape the understanding of the relationship between God the Father, Jesus Christ, and the Holy Spirit. Gregory served as the Bishop of Constantinople and was influential in the early church's efforts to combat heresies. He is celebrated for his contributions to the Council of Constantinople in 381 AD, which affirmed the Nicene Creed. His feast day is observed on January 2 in the Western Church and January 25 in the Eastern Church.