Bishop of Rome vs Ugo Buoncompagni

Bishop of Rome and Ugo Buoncompagni both are nouns.

Word	Noun	Adjective	Verb	Adverb
Bishop of Rome	Yes	No	No	No
Ugo Buoncompagni	Yes	No	No	No

Bishop of Rome (noun)	Ugo Buoncompagni (noun)
the head of the Roman Catholic Church	the pope who sponsored the introduction of the modern calendar (1572-1585)