Calbhach Ó Domhnaill, anglicized Calvagh O'Donnell (died 1566), eldest son of Manus O'Donnell, was an Irish King of Tyrconnell of the mid-16th century. He was Rí and Chief of the O'Donnell dynasty based in Tyrconnell in western Ulster. He is best known for his conflict with Shane O'Neill - a dispute that involved the intervention of the English government in Ireland on Calvagh's side.
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