Eldest son of a Roman noble named Benedict.
Deacon under Pope Stephen V.
Sergius opposed Pope Formosus, but his party was defeated, all their records were destroyed, and most of the surviving documentation about Sergius comes from his opponents.
One of them says he was ordained bishop of Caere by Pope Formosus so he would not become bishop of Rome.
Proposed for the papacy in 896, he was rejected, and retired from his see.
Elected Pope in 897, but exiled by Lambert of Spoleto.
When the antipope Christopher seized the throne by force, the Roman people revolted and threw him from the papacy.
They then invited Sergius to come out of retirement and take the ring of Peter.
He annulled all the ordinations of Formosus.
Restored Saint John Lateran after it was destroyed by fire.
First pope to wear the papal tiara.
His papal flag contained the Croat coat of arms in the shape of a falcon.
One of the worst popes in history, his reign begins the era known as the pornocracy or the rule of the harlots, the darkest period in the history of the papacy.
His mistress Marozia was the mother of Pope John XI, the aunt of Pope John XIII, and the grandmother of PopeBenedict VI.
In addition to Christopher, he killed Pope Leo V in order to obtain the throne, and once in power he had the body of Formosus exhumed, tried, found guilty, and beheaded.