The Armenians first national historiographer.  Under this pen name, he wrote a history of Gregory Illuminator and his apostolic labors as first missionary to the Armenians.  The work exists in Armenian and in Greek.  The Armenian text is entitled: History of the Great Terdat (Tiridates) and of the preaching of St. Gregory the Illuminator, while the Greek text has "Martyrdom of St. Gregory".  The latter work is clearly a version from the Armenian: in the Armenian work there is a long doctrinal discourse of Gregory, equal to one half of the whole work; the Greek translator has suppressed this document.  The author calls himself Agathangelos and says he wrote at the order of king Terdat, not from ancient legends, but as one who had seen and heard what he narrated.  On the other hand, v. Gutschmid has shown that the original Armenian text of Agathangelos belongs to the middle of the fifth century and that it includes fragments of two earlier works: a biography of St. Gregory, and a martyrdom of St. Gregory and of St. Rhipsime and her companions.  One can find in Agathangelos reliable historical material, but he also offers much that is legendary and incredible.  The unknown author seems to have called himself Agathangelos, merely because he related to the Armenians the "good tidings" of the introduction of Christianity among them. (Patrology, Bardenhewer, 1908)