Hrolfr the Northman (Ethelred the Pious)

Hrolfr was a Danish chieftain and a veteran of great raids in France and Ireland. In 895 he settled in England with his wife Poppa, their infant son Vilhjálmr, and a large band of followers. King Hogni of Jorvik let them settle in Devon, at that time a frontier region of Jorvik that was almost 100% Anglo-Saxon. The followers that Hrolfr brought to his new jarldom were a major step in the Norsification of the south.

A restless warrior, Hrolfr led an army into the still independent kingdom of Kernow (Cornwall) in 904. He secured the kingdom's submission and placed his 11-year-old son on the throne. When Hrolfr died, his son Vilhalmer/William spent most of his time in Kernow and gradually lost control of his jarldom in Devon. In 924, King Hogni died, and a number of rival jarls contended for the throne of Jorvik. Vilhalmer's candidate lost to the new king, Bjorn I, and this further hurt his position in England.

His son [Insert Cornish Name] failed to reconquer the Devon jarldom, and thenceforward Hrolfr's descendants ruled Cornwall as an independent Norse-Celtic kingdom. They maintained its independence well into the 11th century.