Saint Gregory of Nyssa was a prominent Christian theologian and bishop in the 4th century. He was born around 335 AD in what is now Turkey and was a key figure in the development of early Christian doctrine. As a member of the Cappadocian Fathers, he contributed significantly to the understanding of the Trinity and the nature of God. Gregory was known for his eloquent writings and sermons, which emphasized the importance of spiritual growth and the pursuit of virtue. He played a vital role in the First Council of Constantinople in 381 AD, helping to affirm the Nicene Creed and combat heresies of the time. His feast day is celebrated on January 10.