I'm curious about Gregorian chants. Who...

There were 16 popes named Gregory, but the one who lent his name to the chants was Pope Gregory I, also known as Gregory the Great (540?-604). He was the father of the medieval papacy and a tremendous influence on his time. Gregorian chant proper is a body of music, purely vocal and ecclesiastical, that evolved from the papal choirs of the fifth and sixth centuries. It was codified in the time of Gregory I and stands as the basis for all Gregorian music.