Cnut

By his death in 1035, King Cnut was the most powerful monarch of Northern Europe. With his father, Swegen Forkbeard, king of Denmark, he invaded England in 1013, driving its king, Aethelred II into temporary exile in Normandy. Aethelred's son, Edmund Ironside, took up the struggle; but the deaths of Swegen and both Aethelred and Edmund in 1016 left Cnut master of the entire kingdom. He subsequently added Denmark itself and Norway to his territories, and probably a part of Sweden too. King Cnut was able, ruthless, and more than just a successful opportunist.