A zealous champion of the veneration of images and the last geat representative of the unity and independence of the Church in the East, b. in 759; d. on the Peninsula of Tryphon, near the promontory Akrita on 11 November, 826. He belonged to a very distinguished family and like his two brothers, one of whom, Joseph, became Archbishop of Thessalonica, was highly educated. In 781 theodore entered the monastery of Saccudion on the Asiatic side of the Bosphorus near Constantinople, where his uncle Plato was abbot. In 787 or 788 Theodore was ordained priest and in 794 succeeded his uncle. He insisted upon the exact observance of the monastic rules. During the Adulterine heresy dispute (see ), concerning the divorce and remarriage of the Emperor Constantine VI, he was banished by Constantine VI to Thessalonica, but returned in triumph after the emperor's overthrow. In 799 he left Saccudion, which was threatened by the Arabs, and took charge of the monastery of the Studium at Constantinople. He gave the Studium an excellent organization which was taken as a model by the entire Byzantine monastic world, and still exists on Mount Athos and in Russian monasticism. He supplemented the somewhat theoretical rules of St. Basil by specific regulations concerning enclosure, poverty, discipline, study, religious services, fasts, and manual labour. When teh Adulterine heresy dispute broke out again in 809, he was exiled a second time as the head of the strictly orthodox church part, but was recalled in 811. The administration of the iconoclastic Emperor Leo V brought new and more severe trials. Theodore courageously denied the emperor's right to interfere in ecclesiastical affairs. He was consequently treated with great cruelty, exiled, and his monastery filled with iconoclastic monks. Theodore lived at Metopa in Bithynia from 814, then at Bonita from 819, and finally at Smyrna. Even in banishment he was the central point of the opposition to Cæsaropapism and Iconoclasm. Michael II (810-9) permitted the exiles to return, but did not annul the laws of his predecessor. Thus Theodore saw himself compelled to continue the struggle. He did not return to the Studium, and died without having attained his ideals. In the Roman Martyrology his feast is placed on 12 November; in the Greek martyrologies on 11 November.

Theodore was a man of practical bent and never wrote any theological works, except a dogmatic treatise on the veneration of images. Many of his works are still unprinted or exist in Old Slavonic and Russian translations. Besides several polemics against the enemies of images, special mention should be made of the "Catechesis magna", and the "Catechesis parva" with their sonorous sermons and orations. His writings on monastic life are: the iambic verses on the monastic offices, his will addressed to the monks, the "Canones", and the "Pœnæ monasteriales", the regulations for the monastery and for the church services. His hymns and epigrams show fiery feeling and a high spirit. He is one of the first of hymn-writers in productiveness, in a peculiarly creative technic, and in elegance of language. 550 letters testify to his ascetical and ecclesiastico-political labours.

Theodorus Studites, Opera varia, ed. Sirmond (Paris, 1696); P. G., XCIX; Nova patrum bibl., V, VIII, IX, X (Rome, 1849, 1871, 1888, 1905); Theodorus Studites, Parva Catechesis, ed. Auvrat-tOUGARD (Paris, 1891); Bibl. hagiogr. Græca (2nd ed., Brussels, 1909), 249; Thomas, Theodor von Studien (Osnabrück, 1892); Gardner, Theodore of Studium (London, 1905).

Klemens Löffler.