Basil and Gregory of Nazianzus, Byzantine fresco

Two brothers and a close friend, these three theologians became defenders of Nicene orthodoxy and carried forward the work of Origen, Tertullian, and Athanasius in formulating the doctrine of the Trinity. The Cappadocian fathers contributed to the emergence of a doctrine of the Trinity that stood between the extremes of Arianism and monarchianism. While Athanasius had emphasized the single substance of the Godhead through the concept homoousios, the Cappadocians accented the idea of hypostasis or "person," which made it possible to speak in a balanced way of the Trinity as a Godhead of one substance and three persons.

Basil the Great (c. 330-379): older brother of Gregory of Nyssa, bishop of Caesarea, and mentor of eastern monasticism. After a brief period of time as a hermit, Basil the Great became bishop of the see of Caesarea and was obliged to take part in the great theological controversies of his era. He became an effective defender of Nicene orthodoxy and of the full divinity of the Holy Spirit. Basil also elaborated the moderate monastic rule which continues to shape eastern monasticism to the present.

Gregory of Nyssa (c. 330-c. 395): younger brother of Basil the Great, bishop of Nyssa, and prolific writer. After a time as a monk, Gregory of Nyssa unwillingly became bishop of Nyssa. He was a prolific author on many theological and pastoral topics, and his works display the influence of neo-platonism and the theology of Origen. Gregory of Nyssa is famed for his use of a simile which suggests that in the incarnation God deceived the devil by using Christ like the bait on a fish-hook.

Gregory of Nazianzus (329-389): bishop of Sasima and later of Constantinople, preacher of Nicene orthodoxy. A monk ordained as a priest and bishop against his will, Gregory of Nazianzus preached powerfully in the cause of Nicene orthodoxy. He wrote extensively on both theological and devotional topics. After the victory of Nicene orthodoxy at the Council of Constantinople I (381), he retired from his dignity as bishop and led a monastic life.