Ethelred (also written Edelred and ETHE-Red) I., fourth king of the Anglo-Saxons, son of Ethelwulf, and successor of his brother Ethelbert, ascended the throne in 866, and died in 871. His reign was a continuous struggle against the Northmen. The sons of the Danish chieftain Ragnar, whom the Northumbrians had put to death, appeared in East Anglia, took possession of the city of York, and defeated and slew two Northumbrian princes who attempted to recover it. Marching southward they took up their winter quarters at Nottingham, whence they retired without a battle after being for some time beleaguered by Ethel-red and his brother Alfred. Passing into East Anglia, they burned on their way the monasteries of Bardney, Croyland, and Medeshamstede, ravaged the nunnery of Ely, and seized and murdered the East Anglian king Edmund, who was hence revered as a martyr. They were met in 871 by Ethelred and Alfred at Reading, but were able to maintain their ground. Being attacked by Alfred four days later at AEscesdun, they were routed and were pursued for a night and a day.

Within a fortnight another battle was fought at Basing, in which the invaders were victorious, and an obstinate engagement soon followed at Merton. Ethelred died of a wound, and left the kingdom to Alfred.