O'Donnell (Irish: Ó Dónaill or Ó Dómhnaill), which is derived from the forname Domhnaill (meaning "world ruler", Rex Mundi in Latin, Modern Irish spelling, Dónall) were an ancient and powerful Irish clan, kings, princes, and lords of Tyrconnel in early times, and the chief allies and sometimes rivals of the O'Neills in Ulster.
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