Cnut the Great, also known as Canute or Knut Sveinsson (Old Norse: Knútr inn ríki; died 12 November 1035) was a Viking king of England, Denmark and Norway. His successes as a statesman, politically and militarily, prove him to be one of the greatest figures of medieval Europe. With his kingship over England's archdioceses, and the continental diocese of Denmark – with a claim lain upon it by the Holy Roman Empire's Hamburg-Bremen archdiocese – and the high status he found among medieval Christendom's magnates, Cnut enjoyed considerable leverage within the Church, winning a number of concessions for his people from the Pope at the coronation of the Holy Roman Emperor.

On a journey to Rome, after his victory against Norway and Sweden, in a letter, Cnut proclaims himself king of all England and Denmark and the Norwegians and of some of the Swedes. The struggles of the kings of Denmark for preeminence within Scandinavia, though, meant Cnut held a considerable overlordship across other areas of the British Isles too, in line with his Anglo-Saxon predecessors, and the leader of a very strong Viking regime.

Uncertain though the extent of his dominance over the British Isles is, Cnut's rule was felt by the sea-kingdoms of the Viking settlers among the Celtic nations, known as the Gall Gaidel. These were the Kingdom of the Isles (probably under direct overlordship through one of his lieutenants, in the Sea of the Hebrides, and the Kingdom of Dublin (probably on the terms of vassal and suzerain), in the Irish Sea. His main aim here was for control of the western seaways to and from Scandinavia, and to check the might of the Earls of Orkney. At the height of his reign, certain Gaelic kingdoms and the dominant Ui Imhair sea-kingdom were in clientage with Cnut too.