Edmund Ironside was King of the English from 23 April to 30 November 1016. He was the son of King Æthelred the Unready and his first wife, Ælfgifu of York. Edmund's reign was marred by a war he had inherited from his father; his cognomen "Ironside" was given to him "because of his valour" in resisting the Danish invasion led by Cnut the Great.
Edmund was not expected to be King of England; however, by June 1014 two elder brothers had died, making him heir apparent. At the end of the same year, England was conquered by Sweyn Forkbeard, who died shortly thereafter. Æthelred was able to reclaim the throne, despite opposition. Sweyn's son, Cnut, was defeated and returned to Denmark, where he assembled an invasion force to re-conquer England. It would not arrive for another year.
After regaining the throne, the royal family set about strengthening its hold on the country with the assistance of Eadric Streona. People who had sided with the Danes in 1014 were punished, and some were killed. In one case, two brothers, Morcar and Sigeferth, were killed and their possessions were taken by Æthelred.