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Diarmait Mac Murchada (also known as Diarmait na nGall, "Dermot of the Foreigners", "Daimait MacMorchada"), anglicized as Dermot MacMurrough (died 1 January 1171) was the King of Leinster, and is often considered to have been the most notorious traitor in Irish history. Ousted as King of Leinster, he invited King Henry II of England to assist him in regaining the throne. The subsequent invasion led to Henry becoming Lord of Ireland himself, and marked the beginning of eight centuries of English dominance.