The Viking adventurer Rollo (ca. 860-ca. 932) founded the line of the dukes of Normandy. He established Viking control of the lands at the mouth of the Seine River and thus began what became the most powerful French dukedom.

Probably born in Norway, Rollo, or Rolf, was the son of Rögnvald, Earl of Möre. Chronicle sources, which are not always reliable, note that he was exiled from Norway because of lawlessness, probably about 900. Rollo became a Viking raider and for a time was successful. He went to Scotland, where he married a Christian woman by whom he had a daughter; and possibly from this marriage his son, later known as William Longsword, his successor in Normandy, also issued. Rollo then may have gone to Ireland, but with the waning of Norse power in Ireland he probably followed his compatriots who traveled to France, where raiding...