Hierarch Saint Gregory, Bishop of Nyssa

Saint Gregory of Nyssa (c. 335 – c. 394) was one of the three great Cappadocian Fathers, the younger brother of Basil the Great and a close friend of Gregory of Nazianzus. Educated in rhetoric, he briefly worked as a teacher and reader before devoting himself to church life. Consecrated bishop of the small Cappadocian town of Nyssa by Basil in 372, he suffered persecution under Arian influence: deposed on a false charge of embezzling church funds in 376, he was restored after Emperor Valens's death in 378.

Following Basil's death in 379, Gregory took up much of his brother's defense of Nicene orthodoxy. He played a significant role at the First Council of Constantinople (381), the Second Ecumenical Council, helping secure the doctrine of the Holy Trinity.

His major works include the "Great Catechetical Oration," "The Life of Moses," and treatises against Eunomius. He is notably the first Christian writer known to have condemned slavery outright as inherently sinful.