Ó Domhnaill is the original Irish Gaelic form of the surname O'Donnell, meaning "descendant of Domhnall." The name Domhnall itself is the Irish form of Donald, derived from the Old Irish elements domun "world" and fal "rule," thus signifying "ruler of the world." The O'Donnell DynastyThe surname is most famously borne by the O'Donnell dynasty (Irish: Ó Dónaill or Ó Domhnaill), a powerful Gaelic Irish clan that ruled the kingdom of Tyrconnell (modern-day County Donegal) in Ulster from the 13th to the early 17th centuries. Like the O'Neill dynasty, the O'Donnells claim descent from Niall of the Nine Hostages, a legendary 5th-century High King of Ireland. Specifically, they trace their lineage to Conall Gulban, a son of Niall, and thus belong to the Cenél Conaill kindred. Conall was reportedly baptized by Saint Patrick, linking the clan's origins to early Christian Ireland. Notable Bearers and Historical SignificanceThe O'Donnell clan played a central role in Irish history, resisting English conquest during the Tudor period. Notable leaders included Cultural SignificanceThe spelling Ó Domhnaill reflects the traditional Irish orthography, with the Ó prefix indicating patronymic descent. Anglicization to O'Donnell occurred during the 17th and 18th centuries, particularly under English administrative influence. The variant forms Mac Domhnaill and McConnell (also Scottish MacConnell) share the same root, while Donnell and Donalds, Donaldson in English and Scottish contexts, are related via Donald. Key Facts Meaning: Descendant of Domhnall (ruler of the world) Origin: Irish Gaelic (Ó Domhnaill) Type: Patronymic surname Usage: Primarily Irish, with Scottish variants Historical Context: Powerful clan in medieval and early modern Tyrconnell