Pope Formosus was the bishop of Rome and ruler of the Papal States from 6 October 891 until his death on 4 April 896. His reign as pope was troubled, marked by interventions in power struggles over the Patriarchate of Constantinople, the Kingdom of West Francia, and the Holy Roman Empire. Because he sided with Arnulf of Carinthia against Lambert of Spoleto, Formosus's remains were exhumed and put on trial in the Cadaver Synod. Several of his immediate successors were primarily preoccupied by the controversial legacy of his pontificate.

Arnulf of Carinthia was the duke of Carinthia who overthrew his uncle Emperor Charles the Fat to become the Carolingian king of East Francia from 887, the disputed king of Italy from 894 and the disputed emperor from February 22, 896, until his death at Regensburg, Bavaria.