Dictionary of National Biography, 1885-1900/O'Brien, Donough (d.1064)
O'BRIEN, DONOUGH (d. 1064), king of Munster, called by Irish writers Donnchadh MacBriain, since he was mac, son, and not ua, grandson, of Brian (926–1014) [q. v.], king of Ireland, from whom the O'Briens (in Irish Uí Briain) take their patronymic. His mother was Dubhchobhlaigh, daughter of the chief of the Sil Muireadhaigh. She died in 1008, and he was her youngest son, and was old enough to lead a foray into Desmond in 1013, and to carry off captive Domhnall, son of Dubhdabhoreann, ancestor of the O'Donoghues. In 1019 he lost the upper part of his right hand in a single combat, and the same sword-cut also wounded his head. In 1026 he obtained hostages in acknowledgment of supremacy from Meath, Ossory, Leinster, and the Danes of the seaports (Annals of Clonmacnoise), but in 1027 he was defeated in Ossory. He burnt Ferns, co. Wexford, in 1041, and in 1044 some of his men plundered Clonmacnoise. He made reparation by giving a grant of freedom from all dues to that church for ever and an immediate gift of forty cows. In 1054 (Annals of Inisfallen) he plundered Meath and the country north of Dublin known as Fingall, and in 1057 made war on his kinsman Maelruanaidh O'Fogarta in Eliogarty, co. Tipperary, and killed him. Dermot Mac Maelnambo, king of Ui Ceinnseallaigh in Leinster, attacked him at Mount Grud in the glen of Aherlagh, co. Tipperary, routed his army, and took much plunder from him. In 1064 he was deposed, went on pilgrimage to Rome, and there died in the same year in the monastery of St. Stephen.
[Annala Rioghachta Eireann, ed. O'Donovan, vol. ii., Dublin, 1851, and the notes contain extracts from the Annals of Clonmacnoise and of Inisfallen; Annals of Ulster, vol. ii. ed. MacCarthy (Rolls Ser.); O'Flaherty's Ogygia, London, 1685.]