John XII (c. 937–May 14, 964), was Pope from December 16, 955 to May 14, 964. The son of Alberic II, Patrician of Rome (932–954), and his daughter Alda of Vienne, he was a seventh generation descendant of Charlemagne on his mother's side.
Before Alberic's death he administered an oath to the Roman nobles in St. Peter's, that on the next vacancy of the papal chair his only son, Octavius, should be elected pope. He succeeded his father as Patrician of Rome in 954, at only seventeen years of age. After the death of the reigning pontiff, Agapetus II, Octavius, then eighteen years of age, was actually chosen his successor on 16 December, 955. His original name was Octavius, but when he assumed the papal see as successor to Pope Agapetus II (946–955), he adopted the apostolic name of John XII. This was the second example of taking a regnal name upon elevation to the papal chair, the first being Pope John II (533–535). Pope John XII was a coarse, immoral man, whose life was such that the Lateran was spoken of as a brothel, and the moral corruption in Rome became the subject of general disgrace.
An account of the charges leveled against him from Patrologia Latina includes:
Then, rising up, the cardinal priest Peter testified that he himself had seen John XII celebrate Mass without taking communion. John, bishop of Narni, and John, a cardinal deacon, professed that they themselves saw that a deacon had been ordained in a horse stable, but were unsure of the time. Benedict, cardinal deacon, with other co-deacons and priests, said they knew that he had been paid for ordaining bishops, specifically that he had ordained a ten-year-old bishop in the city of Todi... They testified about his adultery, which they did not see with their own eyes, but nonetheless knew with certainty: he had fornicated with the widow of Rainier, with Stephana his father's concubine, with the widow Anna, and with his own niece, and he made the sacred palace into a whorehouse. They said that he had gone hunting publicly; that he had blinded his confessor Benedict, and thereafter Benedict had died; that he had killed John, cardinal subdeacon, after castrating him; and that he had set fires, girded on a sword, and put on a helmet and cuirass. All, clerics as well as laymen, declared that he had toasted to the devil with wine. They said when playing at dice, he invoked Jupiter, Venus and other demons. They even said he did not celebrate Matins and the canonical hours nor did he make the sign of the cross.
Enemies defeated him in battle and occupied lands that belonged to the popes. In order to protect himself against the intrigues in Rome and the power of Berengar II of Italy (950–963), John made a deal with Otto I, king of the Germans. He pledged allegiance to Otto and crowned him emperor of the Holy Roman Empire on February 2, 962. In return, Otto promised to recognize only John as pope. Ten days later, the pope and emperor ratified the Diploma Ottonianum, under which the emperor became the guarantor of the independence of the papal states. This was the first effective guarantee of such protection since the Carolingian Empire. After Otto left Rome and reconquered the Papal States from Berengar, however, John became fearful of the emperor's power and sent envoys to the Magyars and the Byzantine Empire to form a league against Otto. His intrigues were discovered by Otto I, who, after defeating and imprisoning Berengar II, returned to Rome. Otto I subsequently summoned a council which deposed John XII, who was in hiding in the mountains of Campania, and elected Pope Leo VIII (963–965) in his stead.
An attempt at a revolt was made by the inhabitants of Rome even before Otto I left the city. Upon his departure, John XII returned at the head of a formidable company of friends and retainers, thus causing Leo VIII to seek safety in immediate flight. The Emperor determined to make an effort in support of Leo VIII, but before he reached the city John XII had died. The manner of his death is uncertain, although it was rumored that he was murdered by a jealous husband whose wife had been discovered receiving the sexual affections of the Pope.