Pope Marinus II

Marinus II became bishop of Rome on 30 October 942, leading the church through the Saeculum obscurum, the "dark age" when Roman noble families controlled the papacy. His three-year reign ended with his death in May 946. Somewhere in the record-keeping, scribes began calling him Martin III instead of Marinus II, an error that stuck so thoroughly that centuries later, when another Martin was elected, he had to take the name Martin IV to keep the sequence. The mistake outlived the man.