Syrian theologian, considered the greatest biblical interpreter of his time and the spiritual head of the exegetical School of Antioch (Antioch, School of).

Theodore studied under the celebrated sophist and rhetorician Libanius with his friend John Chrysostom, who in 369 influenced him to become an ascetic. Entering a monastery near Antioch, he lived and studied there until 378. Ordained in 381, he became bishop of Mopsuestia about 392. He engaged in the contemporary theological controversies plaguing the Eastern church and probably in 402/403 began the writings that made him Antioch's chief spokesman. Theodore wrote commentaries on the Lord's Prayer, the Nicene Creed, the sacraments, and most of the biblical books; he also wrote works on theological and practical problems, such as the Holy Spirit, the Incarnation, priesthood, exegetical method, theological controversies, and monasticism. Theodore's works became normative through their translation into Syriac at Edessa (modern Urfa, Tur.).

As an exegete he used unprecedented critical standards. Instead of the allegorical interpretation employed by the rival exegetical School of Alexandria, Egypt, Theodore used scientific, critical, philological, and historical methods that anticipated modern scholarship. By considering the historical circumstances in which the biblical books were written, he anticipated the modern view that many of the Psalms belong to the 2nd century BC and rejected as uncanonical such books as Chronicles, Esdras, and the Catholic Letters.

Theologically, Theodore insisted that Christ's person has two natures: divine and human. Basing this Christological issue on a psychological analysis of personality, he believed that the human and divine natures were some kind of union, as between body and soul. His Christology opposed that of the Alexandrians and curbed speculation at large through his appreciation of the human nature in Christ and his interest in the literal sense of Scripture. He composed a treatise on allegory and history, no longer extant, in which he criticized Origen, considered the most influential theologian of the early Greek church, for ignoring the literal sense of Scripture. Elsewhere, Theodore said that those who interpreted Scripture allegorically “turn everything backwards, since they make no distinction in divine Scripture between what the text says and dreams.”

Theodore had a strong impact on the Nestorian church, or “the church of the East,” which identified itself with Patriarch Nestorius of Constantinople, whom the Council (431) of Ephesus had condemned. Adhering to the School of Antioch, the Nestorian church called Theodore “the Interpreter” and regarded him as the main authority in all matters of faith. Controversy supported by the Alexandrians climaxed soon after Theodore's death. Though the Council (451) of Chalcedon secured the view of the human nature in Christ, the second Council (553) of Constantinople condemned Theodore's views and writings. After a Persian council in 484 acknowledged him as the guardian of right faith, the church of the East allied with Theodore's theology and has since been Nestorian.