Arnulf of Carinthia was the duke of Carinthia who overthrew his uncle, Emperor Charles the Fat, became the Carolingian king of East Francia from 887, the disputed King of Italy from 894 and the disputed Holy Roman Emperor from February 22, 896 until his death at Regensburg, Bavaria.
Arnulf was the illegitimate son of Carloman, King of Bavaria, and his wife Liutswind, who may have been the sister of Ernst, Count of the Bavarian Nordgau Margraviate in the area of the Upper Palatinate, or perhaps the burgrave of Passau, according to other sources. After Arnulf's birth, Carloman married, before 861, a daughter of that same Count Ernst, who died after 8 August 879. As it is mainly West-Franconian historiography that speaks of Arnulf's illegitimacy, it is quite possible that the two females are actually one and the same person and that Carloman married Arnulf's mother, thus legitimizing his son.
Arnulf was granted the rule over the Duchy of Carinthia, a Frankish vassal state and successor of the ancient Principality of Carantania by his father Carloman, after Carloman reconciled with his own father, king Louis the German and was made king in Duchy of Bavaria.
Arnulf took the leading role in the deposition of his uncle, Emperor Charles the Fat. With the support of the Frankish nobles, Arnulf called a Diet at Tribur and deposed Charles in November 887, under threat of military action.
In September 895 a papal embassy arrived in Regensburg beseeching Arnulf's aid. In October Arnulf undertook his second campaign into Italy. Finding Rome locked against him and held by Ageltrude, Arnulf had to take the city by force on February 21, 896, freeing the pope. Arnulf was then greeted at the Ponte Milvio by the Roman Senate who escorted him into the Leonine City, where he was received by Pope Formosus on the steps of the Santi Apostoli. On February 22, 896 Formosus led the king into the church of St.Peter, anointed and crowned him as emperor, and saluted him as Augustus.
Arnulf retained power in Italy only as long as he was personally there. On his way north, he stopped at Pavia where he crowned his illegitimate son Ratold, as sub-King of Italy, after which he left Ratold in Milan in an attempt to preserve his hold on Italy. That same year pope Formosus died, leaving Lambert once again in power, and both he and Berengar proceeded to kill any officials who had been appointed by Arnulf, forcing Ratold to flee from Milan to Bavaria. For the rest of his life Arnulf exercised very little control in Italy, and his agents in Rome did not prevent the accession of Pope Stephen VI in 896. The Pope initially gave his support to Arnulf, but eventually became a supporter of Lambert.