 The historian Gareth Williams has postulated a kinship link between the mother of Dubgall, Ragnhildis Ólafsdóttir, and the Óttar family which may also have affected Thorfin's political inclinations.Therulfe was the son of Thorfin and grandson of Óttar of Dublin.Following the fall of the Kingdom of Dublin, and a considerable part of the rest of Ireland, to the Anglo-Norman invasion Therulfe took part in an expedition, consisting of 35 ships, mounted by the Ostmen of Cork in 1173 or 1174 against the Normans under Adam de Hereford, deputy to Raymond le Gros.