Diodore of Tarsus (Greek Διόδωρος ὁ Ταρσεύς; died c. 390) was a Christian bishop, monastic reformer, and theologian.
[2] A strong supporter of the orthodoxy of Nicaea, Diodore played a pivotal role in the Council of Constantinople and opposed the anti-Christian policies of Julian the Apostate.
[3] During this period, Diodore's work focused on philosophical treatises and opposing Emperor Julian's attempts to restore paganism in the empire.
Banished to Armenia by Emperor Valens, Diodore encountered a fellow supporter of the Nicene faction, Basil of Caesarea, during his exile.
As bishop of the see of Tarsus, Diodore continued to speak out for the Nicene understanding of the relationship between the human and the divine in the person of Jesus Christ.
When their mentor Meletius died in 381, Diodore recommended his friend Flavian as his successor, thus prolonging the division in the Antiochene church.