Pope Nicholas I

Born around 800, Nicholas became bishop of Rome in April 858 and spent the next nine years turning papal authority from theory into fact. When Lothair II of Lotharingia wanted out of his marriage to Teutberga, a council blessed the annulment; Nicholas declared the council deposed, its envoys excommunicated, and its ruling void. The Carolingians besieged Rome. He didn't budge. His support for the ousted Patriarch Ignatios of Constantinople over his replacement Photius I soured relations with Byzantium, and his insistence that Bulgaria stay under Roman rule - along with disputes over creed and jurisdiction - led the Greeks to excommunicate him at the fourth Council of Constantinople. He died 13 November 867, venerated as a saint since the seventeenth century, the last pope to earn the title "the Great" alongside Leo and Gregory.