Ragnall (d. 921), grandson of Ímar and king of Waterford and York, belonged to a dynasty that had developed close connections with British-based Scandinavians. It is asserted that he was a grandson of Ímar (qv) (d. 873), one of the earliest kings of the Dublin Norsemen. There is no record of his parents, but he had at least three brothers or half-brothers: Ímar (slain 904), Sitriuc Cáech (qv) (d. 927), and Gofraid. As a young man, Ragnall was perhaps among the Scandinavian nobles whom Cerball (qv) son of Muirecán, overking of Leinster, expelled in 902 from Dublin, where his brother Ímar had reigned as king. The party took refuge in Scotland, where Ímar was subsequently slain.
Ragnall came to prominence from 910, when his dynasty defeated the Danes of York and took control of that kingship. In 914 he crushed another rival, Barid son of Ottar, in a naval engagement off the Isle of Man. That same year, he lent dynastic support to a new Scandinavian settlement at Loch Dá Cháech (Waterford harbour) and was soon recognised as ruler of the colony. When the settlers had suffered two setbacks in engagements with the men of Munster, Ragnall took personal charge of their forces in the summer of 917. In August he led reinforcements northwards to Mag Femin (probably the plain of that name in south-east Co. Tipperary), where Niall Glúndub (qv) king of Tara had already engaged with a Scandinavian advance party. A standoff ensued which enabled his brother Sitriuc Cáech to defeat the Leinstermen at Cenn Fuait (probably Glynn, near the River Barrow, parish of St Mullins, Co. Carlow) and take control of Dublin. The following year Ragnall succeeded to the kingship of York, and defeated King Causantín II of Scotland at the second battle of Corbridge, Northumberland. It seems that he reached a modus vivendi with the Scots, which facilitated him in linking the political and commercial interests of Dublin and York.
Ragnall died in 921, apparently of natural causes. He was succeeded at York by Sitriuc Cáech. What transpired in relation to the kingship of Waterford is less clear, although Ragnall's grandson Ímar (qv) features in the annals as rí Phuirt Lairgi (king of Waterford) from before 982 to 1000.