SAHAK (ISAAC) I, the GREAT. - Celebrated Armenian katholikós, born around the middle of the 4th century and probably died on September 7, 439. He was the son of the katholikós Nerses the Great and a true patriarch of Armenian letters. Under his protection and that of Mesrop, the "holy translators" produced the version of Holy Scripture and notable Greek and Syriac writings.
He became katholikós of Armenia around 390 and remained in office until 420, when he was deposed by the Persian emperor Yazdegerd I for maintaining orthodoxy against both paganism and heresy. Nevertheless, he continued to be, as before, the spiritual leader of Armenia. Some years later, he was warned by the bishop of Edessa, Rabbula, of the danger posed by the doctrine of Theodore of Mopsuestia, while other bishops recommended it to him. A national Armenian synod, probably in 435, decided to seek precise information from Proclus of Constantinople, prompting his *Tomus ad Armenios*. Sahak responded to Proclus and to Acacius of Melitene with enthusiasm for orthodoxy and acknowledged the title *Theotokos* for the Virgin Mary. The Armenians venerate Sahak as a saint.
He does not appear to have been a very prolific author, although Koriun attributes to him "many biblical commentaries." Moses of Chorene preserved three of his letters (Armenian History 3.57). Those addressed to Proclus and Acacius are found in the *Book of Letters* (Tiflis 1901); the letter to Proclus was also edited by A. Vardanian in *Wiener Zeitschrift für die Kunde des Morgenlandes*, 27 (1913), pp. 415–411. A canonical constitution attributed to him (cf. F. C. Conybeare, *The Armenian Canons of St. Sahak*, in *The American Journal of Theology*, 2 [1898], pp. 838–438) probably contains an authentic core.