Æthelred the Unready, or Æthelred II, (c. 968–23 April 1016) was King of the English (978–1013 and 1014–1016). He was the son of King Edgar and Queen Ælfthryth and was only about ten years old (no more than thirteen) when his half-brother Edward was murdered. Although Æthelred was not personally suspected of participation, the murder was committed at Corfe Castle by his attendants, making it more difficult for the new king to rally the nation against the military raids by Danes, especially as the legend of St Edward the Martyr grew.

From 991 onwards, Æthelred paid tribute, or Danegeld, to the Danish king. In 1002, Æthelred ordered a massacre of Danish settlers. In 1003, King Sweyn Forkbeard of Denmark invaded England, as a result of which Æthelred fled to Normandy in 1013 and was replaced by Sweyn. He would return as king, however, after Sweyn's death in 1014.

"Unready" is a mistranslation of the Old English word unræd (meaning bad-counseled), a twist on his name "Æthelred", meaning noble-counseled. A better translation would be ill-advised.