Twelfth-century king of Leinster best remembered for bringing the Anglo-Normans to Ireland, c.1169–70, and one of the most execrated names in Irish history. Diarmait eloped with Derbforgaill (2), wife of Tigernán Ua Ruairc [O'Rourke], taking also her substantial dowry, while her husband was on pilgrimage; Derbforgaill may have gone willingly. A traditional date for this elopement is 8 March 1152 or 1156. Tigernán appealed to Tairdelbach Ua Conchobair [Turlough O'Connor], king of Connacht and ard rí, for redress. Tairdelbach forced Diarmait to return Derbforgaill along with her dowry. Later the next ard rí, Ruaidrí Ua Conchobair [Rory/Roderick O'Connor], deposed and banished Diarmait, who fled first to Britain and later to Aquitaine. The Norman-Welsh Richard de Clare, Earl of Pembroke, popularly known as Strongbow, heeded the call, having been promised Diarmait's daughter Aífe. A year after a small preliminary force seized the Danish city of Wexford, May 1169, Strongbow led a large force of armed men to Waterford and Dublin, with the blessings of King Henry II and Pope Adrian IV. Diarmait died in 1171, a year after the taking of Dublin.
The story of Diarmait's treachery has inspired many popular retellings, including one by a president of the United States; see John Quincy Adams, Dermot MacMorrogh, or the Conquest of Ireland (Boston, 1832).
Subjects: Religion — European History.