The Ímar from whom the Uí Ímair are descended is generally presumed to be that Ímar, "king of the Northmen of all Britain and Ireland", whose death is reported by the Annals of Ulster in 873.

Whether this Ímar is to be identified with the leader of the Great Heathen Army or with Ivar the Boneless is less certain.

In the period between the death of Ímar and the expulsion of the Northmen and Norse-Gaels from Dublin in 902, it is not certain that any descendants of Ímar played a notable part in the politics of the region.

Members of the kindred appear to have led armies against the Picts following their expulsion, but these were killed and the armies destroyed in 904 by Constantín son of Áed, the king of Alba.

In the following decade, it is supposed that the grandsons of Ímar may have been in some part of the Atlantic or Irish Sea coasts of Britain where the historical record sheds almost no light on events, the area in question extending from the Isle of Man through the Hebrides to the Northern Isles, as well as the coasts opposite.

They reappear again in 914 when Ragnall and his kinsman Sihtric Cáech are recorded leading fleets in the Irish Sea.

Ragnall defeats the fleet of a certain Barid son of Ottar off the Isle of Man in thus year.

Some historians place the first Battle of Corbridge in this year, following the account in the Historia de Sancto Cuthberto, which can be read as implying two battles, and propose that Ragnall became king of Northumbria in 914 or before.