Gregory the Great
A cardinal who ascended to the papacy in the Vita di Merlino. Merlin had predicted Gregorio’s ascension. During his pontificate, a bishop called Conrad brought a charge of heresy against Merlin, possibly at the instigation of Gregory, but the latter was acquitted.
The author may have been thinking of Pope Gregory I or Saint Gregory the Great (590-604), the earliest Gregory and the closest to the traditional Arthurian period. However, there were twelve other Gregories between Gregory I and Merlino. Gregory sent the Gregorian mission, to evangelize the pagan Anglo-Saxons of England.
Vita di Merlino con le Sue Profetie | c. 1480