Basil the Great, Gregory of Nyssa, and Gregory Nazianzus are considered the Cappadocian Fathers. I have lumped them into one category here to keep my timeline at 50 items.
Basil is the father of Eastern monasticism, though he himself served as a bishop in Caesarea. He wrote On the Holy Spirit, the Hexaemeron, and numerous letters that have helped Christians for centuries.
Gregory of Nyssa, brother of Basil, preferred the life of monasticism, but his brother Basil recruited him as a bishop to fight against Arianism.
Gregory Nazianzus was best friends with Basil, and he was also recruited into the bishopric to fight against Arianism. Together these three helped to facilitate acceptance of the Nicene creed by helping Greek and Latin speakers agree on hypostasis and persona. God is one essence in three persons.
Relative Importance: 80