Pope Sergius IIIMost of what we know about Sergius comes from a history book entitled "Retribution." As you can imagine from the title, the author (a 10th century bishop named Luitprandus) had a few axes to grind.
Be that as it may, his history of Sergius is extremely colorful, alleging that he murdered two men, including one of his papal predecessors, and fathered Pope John XI with his mistress, Marozia, who later became a Roman power broker in her own right.
While these are extreme charges, the crimes are pretty typical of the moral Superfund site that was the City of Rome in medieval times. (See John VIII, John XII, Stephen VII and Leo VIII, among others.) In other words, it's quite possible that Sergius was guilty of everything charged against him and more. Some accounts also accuse Sergius of re-creating the "Cadaver Synod" of Stephen VII, digging up the body of a former pope for the second time and beheading it, just to be an asshole.
Sergius was Roman-born, but little is known of his early life. He was made bishop by Pope Formosus, a controversial political pope of the 9th century who probably gave Sergius the post in the hopes of shutting him up. In the end, Sergius allied himself with the enemies of Formosus, who were many in number and extremely cranky.
After the death of Formosus in 896, the papacy went into freefall as two competing factions—basically pro-Formosus and anti-Formosus—struggled to seize power in Rome. From Formosus to Sergius III, there were nine popes in less than eight years. Very few of these regime changes can be credibly attributed to death by natural causes.
In 896, Stephen VII put the conflict into sharp relief by digging up the corpse of Formosus, putting it on trial, convicting it and stripping it of its papal rank. Aside from its merit as a psychotic episode, the upshot of this was to void all the ordinations and appointments made by Formosus so that the anti-Formosus crowd could take power.
Sergius was elected to succeed Stephen, but he was instantly usurped. After a few false starts, the pro-Formosus crowd installed John IX as pope, who excommunicated Sergius and reinstated Formosus.
At the time, excommunication was a popular form of political attack, but it was rendered virtually meaningless by the back-and-forth excommunications and recommunications of the post-Formosus era. The pendulum went back in the direction of the anti-Formosians, and Sergius found himself back in good grace, both literally and figuratively. When Sergius III took office in 904, however, it represented the big comeback of the anti-Formosus crew. The historical accounts differ on whether Sergius literally dug Formosus out of his grave yet again (possibly beheading the corpse in the process), but he did void all of the Formosus appointments yet again, in defiance of the previous papal edicts banning posthumous persecution.
The reign of Sergius marked the beginning of Rome's first "pornocracy", so named because Sergius and several popes after him were believed to be puppets under the control of a female Roman senator named Theodora, and her daughter, Marozia.
Whether Theodora and her daughter were actual harlots, as there enemies claimed, or merely prototypes for Hillary Clinton, we will never know. All the histories were written by the enemies of Sergius, so let's stipulate that right now and get down to the juicy gossip.
Sergius was reportedly doing both Theodora and Marozia, who was a ripe 14 at the time Sergius became pope. On taking office, Sergius set about consolidating his power with ruthless abandon. Two of his predecessors—Pope Leo V and Pope Christopher, who had taken the papacy by military force and was only semi-legitimate—were in prison when Sergius became pope. Both were soon deceased, allegedly at the order of Sergius himself.
Theologically, Sergius did little to distinguish himself, although he was said to be a proponent of the filioque, an incredibly arcane doctrine which nails down the metaphysical mechanics of exactly how the Holy Ghost "proceeds" from the Father and the Son in the Trinity. As any fool can see, the ramifications of getting this process wrong would be utterly disastrous, so you can thank Sergius for straightening out that issue and saving all our souls.
At any rate, Sergius and most of his contemporaries were less concerned with religion than politics. After the initial ruckus over Formosus, the reign of Sergius was apparently relatively uneventful. He was pope for seven years before dying in 911.
Sergius fathered a child with the young Marozia, who later rose to political power like her mother. Marozia installed her son as Pope John XI, but her younger son, Alberic, seized control of Rome and reduced John to a figurehead. Which just goes to show that popes shouldn't breed, in case you hadn't already figured that out.