From the LCMS website:
Basil and the two Gregorys, collectively known as the Cappadocian Fathers, were leaders of Christian orthodoxy in Asia Minor (modern Turkey) in the later fourth century. Basil and Gregory of Nyssa were brothers; Gregory of Nazianzus was their friend. All three were influential in shaping the theology ratified by the Council of Constantinople of 381, which is expressed in the Nicene Creed. Their defense of the doctrines of the Holy Spirit and Holy Trinity, together with their contributions to the liturgy of the Eastern Church, make them among the most influential Christian teachers and theologians of their time.
For even more on the Cappadocian Fathers, check out Cyberbrethren, where you’ll find information on their lives and writings.