http://en.wikipedia.org/wiki/Edmund_II_of_England

Edmund Ironside or Eadmund , surnamed "Ironside" for his efforts to fend off the Danish invasion led by King Canute, was King of England from 23 April to 30 November 1016.

Edmund was the second son of King Æthelred II and his first wife, Ælfgifu of Northumbria. He had three brothers, the elder being Æthelstan, and the younger two being Eadred and Ecgbert. His mother was dead by 996, after which his father remarried, this time to Emma of Normandy.
Æthelstan died in 1014, leaving Edmund as heir. A power-struggle began between Edmund and his father, and in 1015 King Æthelred had two of Edmund's allies, Sigeferth and Morcar, executed. Edmund then took Sigeferth's widow, Ealdgyth, from Malmesbury Abbey where she had been imprisoned and married her in defiance of his father. During this time, Canute the Great attacked England with his forces. In 1016 Edmund staged a rebellion in conjunction with Earl Uhtred of Northumbria, but after Uhtred deserted him and submitted to Canute, Edmund was reconciled with his father.