Timothy I (727-823), Patriarch of Baghdad and head of the Assyrian Church of the East from 779, was a writer of scientific, theological, liturgical, and canonical books. Timothy is first noted as the bishop of Beth Bagash in 769/770. Some 59 of his letters survive, covering roughly the first half of his patriarchate. The letters discuss varied Biblical and theological questions as well as revealing much about the situation of the church in his day. One letter records him ordaining bishops for the Turks, for Tibet, for Shiharzur, Radan, Ray, Iran, Gurgan, Balad, and several other places. The letters also show a wide familiarity with literature from across the ancient Christian world. Because he moved to Baghdad after his election as patriarch, he was familiar with the Abbasid court and assisted in the translation of works by Aristotle and others. He also held a dialogue in 782 AD with the 3rd Caliph al-Mahdi.
Raphaël J. Bidawid, Les Lettres du Patriarche Nestorien Timothée I, Studi e Testi 187 (Vatican: Biblioteca Apostolica Vaticana, 1956).
Erica C. D. Hunter, Interfaith dialogues: The Church of the East and the Abbassids, in Der Christliche Orient und seine Umwelt ed. S.G.Vashaolmidze and L. Greisiger, Harrassowitze (2007), pp.289-302.