Ó Domhnaill is a prominent Irish surname, meaning "descendant of Domhnall," with roots in the Gaelic language. It is associated with the O'Donnell clan, which was historically significant in County Donegal, Ireland. The clan played a crucial role in Irish history, particularly during the 15th and 16th centuries. The Ó Domhnaill family was known for its leadership and resistance against English rule. The most famous figure from this lineage is Hugh O'Donnell, who was a key leader during the Nine Years' War. Today, the name remains common in Ireland and among the Irish diaspora worldwide.