THEORIANOS. – A Byzantine writer of the 12th century. Emperor Manuel I Komnenos (1143–80) twice dispatched him, in 1170 and 1172, as his delegate to the Armenian patriarch Nerses II for negotiations on union, which proved fruitless, between the Byzantine Church and the Armenian Church. He also engaged in a religious disputation with the Jacobites. Documents relating to this activity still survive. T. adopted a conciliatory stance on the question of the use of unleavened bread and maintained a firm and decisive position against Monophysitism.
BIBL.: PG 133, 113–298; A. Mai, Scriptorum veterum nova collectio, VI, I, Rome 1854, pp. 314–87; R. J. Loenertz, L'épithet de Théorien le philosophe aux prêtres d'Orléans, in Memorialis Poëtri, Bucharest 1948, pp. 317–35.