Which Viking king ruled England, Denmark and Norway in the early 11th century?

The Viking king who ruled England, Denmark and Norway in the early 11th century was Cnut the Great.

Cnut, also written Canute, became king of England in 1016 after defeating Edmund Ironside. He inherited Denmark after the death of his father, Sweyn Forkbeard, and later established control over Norway. This created a powerful North Sea empire linking Scandinavia and England.

Cnut promoted Christianity and worked with the English Church while retaining the political practices of a Scandinavian ruler. He married Emma of Normandy, the widow of Æthelred the Unready, strengthening his claim and connecting his dynasty with Norman and English politics.

His empire did not survive long after his death in 1035. His sons ruled different parts of the realm, but succession disputes weakened the political union. Cnut is sometimes called the first ruler of a North Sea Empire, although that modern label describes a personal monarchy rather than a centralized state.