The noun has 3 meanings:
Meaning #1:
the pope who sponsored the introduction of the modern calendar (1572-1585)
Synonyms: Gregory XIII, Ugo Buoncompagni
Meaning #2:
the pope who fought to establish the supremacy of the pope over the Church and the supremacy of the Church over the state (1020-1085)
Synonyms: Gregory VII, Hildebrand
Meaning #3:
the pope for whom Gregorian chants were named (circa 540-604)
Synonyms: Gregory I, Saint Gregory I, St Gregory I, Gregory the Great




