Founder of the church at Edessa. He was allegedly one of the seventy disciples of Jesus sent to King Abgar V Ukkama by the Apostle Thomas after the Ascension. Eusebius records the legend and calls Addai “Thaddaeus.” The Syriac Doctrina Addaei was published in 1876. The conversion of King Abgar IX (179-216) points more reliably to evangelism at Edessa, possibly in the late second century, by a Jewish Christian Addai (Baus, Handbook of Church History, vol. 1, p.207).

See Abgar, Legend of.