Anastasius Bibliothecarius is a Roman Catholic Bishop and the main antagonist in the 2009 film Pope Joan.
During the reign of Pope Sergius II Anastasius was appointed the Papal Nomenclator, a highly placed advisory second only to the Pope.
By the mid 840s Sergius was bedridden with a serious illness. As Sergius got sicker he left the business of running the church to Anastasius, who became Pope in all but name. Healers in the employ of the Vatican tried treating the Pope, however he had not responded well to treatments - which included bloodletting. Anastasius - who with his father Arsenius were seeking to get Anastasius elected as Pope - thought the sooner Sergius died the better. However Arsenius counseled that Anastasius, who was not currently well loved by the Roman populace, should work to save the Pope as a means of increasing his popularity with the Romans and making it more likely that he would someday succeed Sergius to the throne.
Meanwhile a young woman named Johanna, who was disguised as a young male monk named Johannus Anglicus, had arrived in Rome and began healing people. News of this reached the Vatican, and Anastasius sent for Johannus Anglicus. When she arrived at the Vatican the healers tested her by giving her urine from a pregnant woman to ensure she had medical knowledge. Johanna took one taste of the urine and wryly remarked that it was a miracle, that the Pope was with child, thus passing their test.
Seeing the Pope's condition, she correctly deduced that he was suffering from gout. She gave him medicine to take away the pain and to help him get the sleep he needed. Under her care the Pope rapidly improved to the point that he was able to start attending meetings again and overrode some of the decisions Anastasius had made while he was ill.
After Serguis was able to successfully face down the Holy Roman Emperor and make peace with him, Serguis began planning to replace Anastasius with Johanna as his Papal Nomenclator. This was too much for Anastasius to tolerate, and he arranged for Sergius to be poisoned.
With Serguis now dead the populace of Rome held the election of the Pope as was the practice at the time. Anastasius was one of nominees to become the next Pope, and was appearing to being well on his way to becoming Pope when another nominee was put forward - Johannus Anglicus. Johanna and her lover Gerold had been planning to flee the city since the election of Anastasius would mean her death in very short order, but officials delivered the shocking news that she had just been elected Lord Pope.
Anastasius was not happy over the election of a seemingly young man who could conceivably be Pope for decades. Arsenius at this point felt that maybe this was divine punishment against them for coveting the office of Pope.
Gerold and Johanna soon learned that their lovemaking had led to Johanna becoming pregnant. Knowing that even though she was a popular Pope the Romans would never tolerate her presence if the fact that she was a pregnant woman became public knowledge. She and Gerold decided to disappear but not until after Easter. A short time later Gerold was soon murdered on the streets of Rome. A short distance away Johanna gave birth on a public street, followed by her collapsing and dying.
Anastasius was elected Pope immediately afterwards. However his reign as Pope was not long, as the people of Rome rebelled against Anastasius, deposed him, and exiled him to a monastery. While there Anastasius wrote the Liber Pontificalis, a list of all the Popes up to the present. He omitted Johanna from the list of Popes, however Bishop Arnaldo of Paris, another woman disguised as a male, wrote a history of Joan and ensured its placement in the Liber Pontificalis.