This man's aunt Gunhilde was reportedly slain in the St. Brice's Day Massacre, which was directed against this man's people.
One legend says this man allowed a wave to hit him as a way to prove to his followers that God was more powerful than he.  He won the Battle of Assandun, forcing a negotiated settlement that set the Thames as a temporary boundary. This man's aunt Gunhilde was reportedly slain in the St. Brice's Day Massacre, which was directed against this man's people. He dispatched his consort, Aelfgifu, to serve as a harsh regent in Norway. This ruler married Emma of Normandy, widow of Ethelred the Unready, and led Danish troops in defeating Ethelred's son, Edmund Ironside, eventually becoming king of all England. For 10 points, name this son of Sweyn Forkbeard, who ruled England from 1016 to1035, and who was known as the "great."
One legend says this man allowed a wave to hit him as a way to prove to his followers that God was more powerful than he.  
{Canute} the Great [or {Cnut}, {Knut}, {Knud}]