Eowils and Halfdan were joint Kings of Northumbria

Northumbria

Northumbria was a medieval kingdom of the Angles, in what is now Northern England and South-East Scotland, becoming subsequently an earldom in a united Anglo-Saxon kingdom of England. The name reflects the approximate southern limit to the kingdom's territory, the Humber Estuary.Northumbria was...

, in England.

Their reign began with the death of Æthelwold of Wessex

Æthelwold of Wessex

Æthelwold was the youngest of three known sons of King Æthelred of Wessex. His brother Oswald is recorded between 863 and 875, and Æthelhelm is only recorded as a beneficiary of King Alfred's will in the mid 880s, and probably died soon afterwards...

, killed by Edward the Elder

Edward the Elder

Edward the Elder was an English king. He became king in 899 upon the death of his father, Alfred the Great. His court was at Winchester, previously the capital of Wessex...

 after Æthelwold's Revolt

Æthelwold's Revolt

Æthelwold's Revolt was an attempt by Æthelwold of Wessex to seize the throne from Edward the Elder after the death of Alfred the Great.- Background :...

 in 902. They ruled the Danish Kingdom for over 8 years before meeting the English King themselves at the Battle of Tettenhall

Battle of Tettenhall

The Battle of Tettenhall took place, according to the Anglo Saxon Chronicle near Tettenhall, on the 5 August 910. The allied forces of Mercia and Wessex met an army of Northumbrian Vikings in Mercia...

. Both Eowils and Halfdan were left dead on the field as the Viking army was decisively defeated by allied English forces.

The co-Kings were succeeded by Ragnall ua Ímair

Ragnall ua Ímair

Ragnall was a Norse overlord or emperor of northern Britain, including Northumbria, the entire Irish Sea region including the Isle of Man, south to Waterford and briefly much of the Irish province of Munster, and then returning to Britain, briefly York as distinct from Northumbria at this time...

.