The name is derived from two elements: one is the Old Scandinavian personal name Ragni; the other element is the Old English hyll, meaning "hill".
After Somerled's death in 1164 his kingdom was split between his three sons, Ragnall in Islay and Kintyre, Dughall in Lorne and the other Argyll islands, and Angus holding Arran and Bute.