Pope, succeeded Nicholas I. A. D. 867. Having twice refused the dignity, he accepted it in the 76th year of his age, at the united request of the clergy, nobility, and people. The contest for power between the Greek and Latin churches had been very violent some years before his accession to the papal chair.

Adrian, during this contest with the eastern patriarch, was extending his authority over the kings and princes of the west. He employed his whole interest to induce Charles the Bald, who had taken possession of the kingdom of Lorraine, and who had been crowned at Rheims by the archbishop Hinemar, to relinquish it in favour of the emperor; and he even sent legates to the king, after having attempted to engage Hinemar, the clergy, and the nobility, to desert him, ordering him to surrender to the emperor's right. The king was invincible; and the pope was obliged to give up the contest. He also farther interfered in the concerns of princes, by taking Charles's rebellious son Carloman, and the younger Hinemar, bishop of Laon, under the protection of the Roman see. He proceeded in this business so far, that he was under the necessity of submitting without gaining his point. Death terminated his ambitious projects and his life of iniquity, A. D. 872, after a pontificate of five years.