Gregory I may refer to: Gregory the Illuminator (250s–330s), Catholicos of the Armenian Apostolic Church in 288–325 Gregory of Nazianzus (329–390), Patriarch Gregory I of Constantinople, in office 379–381 Pope Gregory I (540–604), in office 590–604 Gregory I of Naples (died 755), r. 740–755 Gregory I, Patriarch of Bulgaria c. 940 – c. 944 Gregory I, Count of Tusculum, r. in 954–1012 Patriarch Gregory I of Alexandria, Greek Orthodox patriarch, in office 1354–1366 Maputeoa (1814–1857), Gregorio I Maputeoa, King of Mangareva, r. c. 1830–1857