Who he was
Sergius was a Roman of noble birth, the son of Benedict, and was made Bishop of Cerveteri by Formosus, though he seems to have stopped acting as a bishop after Formosus died. He was put forward for the papacy in 898 but lost to John IX and withdrew from Rome. In 904 the Romans, having imprisoned the usurper Christopher, called him back, and he was consecrated on 29 January.
What he is remembered for
As a leader of the party opposed to Formosus, he declared Formosus's ordinations invalid, which caused much confusion. He restored the Lateran Basilica completely, protected the Archbishop of Ravenna, and accepted the Greek Emperor Leo VI's fourth marriage as valid. Nearly all that was written about him comes from his opponents, and the Catholic Encyclopedia regards their worst charges as very doubtful.
Sources
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