King Æthelred II (pictured) ordered the massacre of all Danes in England.

Æthelred II, known as Æthelred the Unready, was King of the English from 978 to 1013 and again from 1014 until his death in 1016. His epithet comes from the Old English word unræd meaning "poorly advised"; it is a pun on his name, which means "well advised".

The St. Brice's Day massacre was a mass killing of Danes within England on 13 November 1002, on the order of King Æthelred the Unready of England. The Anglo-Saxon chronicle relates that the massacre was carried out in response to an accusation that the Danes would "beshrew [Æthelred] of his life, and afterwards all his council, and then have his kingdom without any resistance." King Æthelred thus ordered the killing of many Danes within his territory. The retaliation by the Danish King Sweyn Forkbeard over the next few years would earn Æthelred the nickname Æthelred the Ill-Advised.