According to Æthelweard's Chronicon he was a co-king of Northumbria along with his brothers Eowils and Halfdan, though the Anglo-Saxon Chronicle does not mention him.
The population of the Danelaw was boosted in 902 by the arrival of the Vikings of Dublin who were ejected from the city that year.
No coins bearing their names are known and it is possible they each ruled different parts of Northumbria, or even that they were simply commanders in the Viking army rather than kings, and their identification as such by contemporary sources is erroneous.
[3] Ingwær is known to history through Æthelweard's Latin version of the Anglo-Saxon Chronicle; in the extant Old English manuscripts he does not appear, only his brothers Eowils and Halfdan.
David Dumville has suggested this similarity could indicate Ingwær, Eowils and Halfdan are from the same family as the earlier trio, the Uí Ímair.