 As late as the late 19th century, it was claimed that the clan descended from Alasdair Òg, son and heir of Aonghas Mòr, son and heir of Dòmhnall (died mid 13th century), the eponymous ancestor of Clan Donald.However a more modern understanding is that the clan's eponymous ancestor is Alasdair Mòr (died 1299), younger son of Dòmhnall (eponymous ancestor of Clan Donald).Bearers of the Irish "Mac Alastair", and its various Anglicised forms, include descendants of Clan Donald who settled in what is today County Antrim, Northern Ireland.