Donnchad Donn mac Flainn

Donnchadh Donn mac Flainn (older spelling: Donnchad Donn mac Flainn) (Duncan of the Brown Hair, son of Flann) (died 944) was High King of Ireland and King of Mide. He belonged to Clann Cholmáin, a branch of the southern Uí Néill.

Donnchad was the son of High King Flann Sinna by his wife Gormlaith ingen Fhlainn maic Conaing. The date of his birth is not known, but he was apparently an adult in 904 when he is found as the leader, or figurehead, of a challenge to his father at Kells. The Annals of Ulster state that many of Donnchad's associates were beheaded by Flann, and that the High King profaned the sanctuary at Kells to seize Donnchad.

Donnchad again rebelled against his father in 915, with the support of his brother Conchobar, but this rebellion was suppressed by his sister's Gormlaith's husband, and his father's heir, Niall Glúndub. When Flann died in 916, Niall Glúndub succeeded him as King of Tara, while Conchobar became King of Mide, the kingship of Clann Cholmáin.

Niall and Conchobar were both killed on 14 September 919, in battle against the Foreigners—Vikings and Norse-Gaels—at Dublin. Other Irish kings and princes among the dead were another of Donnchad's sister's husbands, Máel Mithig mac Flannacáin, Niall Glúndub's brother's son and heir-designate Flaithbertach mac Domnaill, "and many other nobles".

Donnchad succeeded to the kingship of Mide, and to the high kingship of Ireland. He immediately had his brother Áed blinded. Two years later, Donnchad disposed of another brother, the annals saying: "Domnall grandson of Máel Sechnaill was deceitfully killed by his brother Donnchad, which was fitting." Some years later, Donnchad disposed of his nephew, Máel Ruanaid, Conchobar's son.

Donnchad's first venture was a campaign against armies of the Foreigners in modern County Louth, "in which a very large number [of the Foreigners] were slaughtered." The majority of the reports of battles with the Foreigners thereafter in Donnchad's reign concern "the Hector of the western world", the indefatigable Muirchertach mac Néill—Muirchertach of the Leather Cloaks—the King of Ailech and likely to have been Donnchad's successor had he not died in battle against the Foreigners on 26 February 943. Donnchad's relations with Muirchertach, his daughter's husband, were not good, and conflict between them is recorded in 927, 929, and 938. Muirchertach's wife died in 940, and in 941 he raided Mide, Osraige, and Munster, taking the Munster king Cellachán Caisil hostage as a demonstration of his power, and Donnchad's limited authority.

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