Head of the Catholic Church from 858 to 867
Source (Wikipedia): Pope Nicholas I

Pope Nicholas I, called Nicholas the Great, was the bishop of Rome and ruler of the Papal States from 24 April 858 until his death. He is remembered as a consolidator of papal authority, exerting decisive influence on the historical development of the papacy and its position among the Christian nations of Western Europe. Nicholas I asserted that the pope should have suzerainty over all Christians, even royalty, in matters of faith and morals.