Throughout his life he maintained letter correspondences with many important political and cultural figures of the Byzantine empire;[3] this included many women, such as the composer and nun Kassia, who was much influenced by his teachings.

[10] According to the later hagiographical literature, Theodore received an education befitting his family's station and from the age of seven was instructed by a private tutor, eventually concentrating in particular on theology.

[11] Following the death of Emperor Leo IV (r. 775–780) in 780, Theodore's uncle Platon, who had lived as a monk in the Symbola Monastery in Bithynia since 759, visited Constantinople, and persuaded the entire family of his sister, Theoktiste, to likewise take monastic vows.

Theodore, together with his father and brothers, sailed back to Bithynia with Platon in 781, where they set about transforming the family estate into a religious establishment, which became known as the Sakkudion Monastery.

[16] This demand had no official weight, however, and Constantine appears to have attempted to make peace with Theodore and Platon (who, on account of his marriage, were now his relatives), inviting them to visit him during a sojourn at the imperial baths of Prusa in Bithynia.

[18] The monks arrived in Thessaloniki in March 797, but did not remain for long; in August of the same year Constantine VI was blinded and overthrown, and his mother Irene, the new empress, lifted the exile.

He maintained contact with these other monasteries above all through his prodigious literary output (letters as well as catechisms), which reached a quantitative peak at this time, and developed a system of messengers that was so elaborate as to resemble a private postal service.

[28] The selection of Nikephoros gave rise to an immediate protest on the part of the Studites, and in particular Theodore and Platon, who objected to the elevation of a layman to the patriarchal throne.

[30] Therefore, relations between the Studite Abbot and the Patriarch appear to have been initially untroubled, an impression which is reinforced by the choice (806/807) of Theodore's brother, Joseph, as Archbishop of Thessaloniki.

[37] Theodore maintained an extensive literary activity in exile, writing numerous letters to correspondents including his brother, various Studite monks, influential family members, and even Pope Leo III.

[41] Michael led a military campaign against the Bulgarians in 813, which ended in defeat, and as a result he abdicated in July and Leo V was crowned emperor.

[43] At the very beginning of his reign, the emperor Leo V faced a new Bulgarian offensive that reached the walls of Constantinople and ravaged large sections of Thrace.

[44] However, as the previous 30 years since the approval of icon-veneration at the Synod of 787 had represented for the Byzantines a string of military catastrophes, Leo resolved to reach back to the policies of the more successful Isaurian dynasty.

This movement met with strong opposition from the Patriarch Nikephoros, who himself gathered a group of bishops and abbots about him and swore them to uphold the veneration of images.

The dispute came to a head in a debate between the two parties before the emperor in the Great Palace in early 815, at which Theodore and his brother Joseph were present and took the side of the iconodules.

[48] While Theodore was in exile, the leadership of the Studite congregation was assumed by the Abbot Leontios, who for a time adopted the iconoclast position and won over many individual monks to his party.

Early in 821, however, Leo V fell victim to a grisly murder at the altar of the Church of St. Stephen in the imperial palace; Theodore was released from exile shortly thereafter.

[58] An imperial audience was arranged for a group of iconodule clerics, including Theodore, at which however Michael expressed his intention to "leave the church as he had found it."

[60] He was present at a meeting of "more than a hundred" iconodule clerics in 823 or 824, which ended in an argument between the Studites and the host, one Ioannikos, which may have represented a power struggle within the movement.

[61] Theodore also spoke against the second marriage of Michael II to the nun Euphrosyne, a daughter of Constantine VI, although in a very moderate fashion, and with none of the passion or effect of the Moechian controversy.

His disciple, Naukratios, recovered control of the monastery after the end of iconoclasm in 842, and throughout the remainder of the ninth century the Studite abbots continued Theodore's tradition of opposition to patriarchal and imperial authority.

[68] Theodore also built the Stoudios monastery into a major scholarly center, in particular through its library and scriptorium, which certainly surpassed all other contemporary Byzantine ecclesiastical institutions in this regard.

In the Latin West, Theodore’s recognition of papal primacy on the basis of his letters to Pope Paschal I was part of what caused him to be formally canonized by the Catholic Church.

It was not until the ninth century after, that one of his humble followers, Saint Theodore of Studium (Constantinople), ventured to put forth the command "Thou shalt possess no slave, neither for domestic service nor for the labor of the fields, for man is made in the image of God."