Donnchad (d. 1064), son of Brian, was a son of Brian Bórama (qv) and his wife Gormlaith (qv) (d. 1030), daughter of Murchad son of Finn of the Uí Fháeláin; she had previously been married to Amlaíb (Óláfr) Cuarán (qv), king of Dublin. Among his wives were another Gormlaith, daughter of Ua Donnacáin, king of Ara Tíre, and a daughter of Ragnall grandson of Ímar (qv) (d. 1000), viking king of Waterford, whom he married in 1032.
As his father's eldest son, Donnchad was involved in the lead-up to the battle of Clontarf; that Brian should send him to attack Leinster during the encounter itself, however, may suggest a lack of confidence on the part of his father in his military abilities. In any event, later traditions claim that it was another son, Murchad, rather than Donnchad, whom Brian wished to succeed him. If so, Murchad's heroic death, alongside his father, at Clontarf brought Donnchad to power, although it was over a much depleted territory that he began his reign. Nor did that reign begin auspiciously, with Donnchad being assailed by Munster neighbours, the Éoganacht Raithlind, as well as by his half-brother, Tadc, before the end of his first year in power. His second year (1015) saw him similarly arrayed against the Éoganachta. Of greater import, however, was the continuation of civil war within his own territory which culminated in a murder attempt on him by the Uí Chaisín four years later and the slaying, at his instigation, of his principal rival, Tadc, in 1023. The latter event, coupled with the death of his main external opponent, Máel-Sechnaill (qv) (d. 1022) son of Domnall, made it easier for him to attempt to extend his authority in subsequent years.
Donnchad was not slow to take advantage of the new political situation. He may have been active in Leinster in 1024, though the Munstermen were defeated. He had more success in Connacht the following year, returning with hostages. To these he added hostages from Mide, Brega, Dublin, Leinster and Osraige in 1026, making him effective ruler of the southern part of Ireland. Indeed, about this time he is termed ‘king of Ireland’ on the shrine of the Stowe Missal constructed on his behalf. This hard-won authority was not to endure in the face of the growing strength of Osraige, under Donnchad (qv) son of Gilla-Pátraic, and more significantly of Leinster, led by Donnchad's own son-in-law, Diarmait (qv) son of Donnchad Máel na mBó (qv). It was the latter's cultivation of his foster-son, the Munster king's nephew, Tairdelbach Ua Briain (qv) (d. 1086), son of the murdered Tadc, that led to Donnchad's ultimate downfall.
Decades of struggle preceded his demise as he failed to halt the increasingly frequent incursions of Donnchad son of Gilla-Pátraic into Munster territory, which was made easier by an alliance between Osraige and Éoganacht Chaisil. Thus, he was powerless to prevent the destruction of his strategically placed fortress, Dún na Sciath, in 1031; an attempt to exact revenge in Osraige territory ended in defeat. Bolstered by their new-found friends, the Éoganachta too proved restless and, together with the Osraige, made another attack on Dún na Sciath in 1043. Diarmait son of Máel na mBó, however, was soon to prove a greater threat, with frequent forays southwards by Áed Ua Conchobair (qv), king of Connacht, complicating matters. Although Donnchad managed to obtain Diarmait's hostages in 1048 and again the following year, he failed to subdue Connacht. In a very public display of his authority, Áed destroyed bile Maige Adair, the sacred tree of the Dál Cais, in 1050 and a year later engaged in an encounter with the Munstermen in which Donnchad's son, Domnall Bán, was slain.
Leinster and Connacht allied against Donnchad in 1054, perhaps at the request of Donnchad's nephew, Tairdelbach, who was now actively campaigning against his uncle. Thus, with the support of Ua Conchobair, he plundered Donnchad's home territory of North Munster, while Diarmait son of Máel na mBó, allied with Osraige, burned one of Ua Briain's fortresses at Dún Trí Liac. The onslaught continued the following year. When Tairdelbach attacked Donnchad's forces in Clare, Diarmait's Dublin allies came to his aid, plundering Scattery Island in 1057, while one year later Tairdelbach himself stood shoulder to shoulder with his Uí Chennselaig patron at the head of an army including the Dublin men, as well as the forces of Leinster and Osraige. Rather than see Limerick fall to his enemies, Donnchad burned the city himself. It was to no avail, however, since he suffered a humiliating defeat in the battle of Sliab Crot at the hands of Diarmait; the latter's aim was to set up Tairdelbach as a pliant and subordinate king of Munster (Ó Corráin, Ireland before the Normans, 135). And while Tairdelbach did not officially assume the kingship till 1063, Donnchad was in fact a spent force from this time onwards.
In 1059 he was powerless to resist another attack by Diarmait, and the following year he was forced to submit to Áed Ua Conchobair. Shortly afterwards, however, he turned his allegiance to the Leinster ruler, as a result of which Ua Conchobair burned Killaloe and destroyed Donnchad's fort at Kincora. The alliance between Diarmait and his foster-son remained as strong as ever; he and Tairdelbach plundered Munster again in 1062, seeing off the resistance of Donnchad's son, Muirchertach, with ease and they burned Limerick the following year. Seeing the writing on the wall, Donnchad's vassals sought out Tairdelbach and it was to this younger Ua Briain that Diarmait gave the hostages of Munster later that year: a new era had begun.
Donnchad's brief retirement was spent in Rome, where he went on pilgrimage with his brother-in-law, Echmarcach (qv) son of Ragnall, in 1064, dying there before the end of the year. It was not his first encounter with religion: according to the Annals of Inisfallen, he was involved in enacting ecclesiastical legislation in the year 1040, when he ordained that ‘none should dare to steal, or do feats of arms on Sunday, or go out on Sunday carrying any load’. How influential his cána (laws) may have been is not known; in general, however, his political activities were overshadowed by those of more successful contemporaries. Moreover, as son and successor to Brian Bórama, during whose reign the Dál Cais were transformed into players on a national scale, and immediate ancestor of a nephew, Tairdelbach, and grandnephew, Muirchertach (qv), who ensured that the Uí Briain remained centre stage, history has accorded him something of a caretaker role. Yet for much of his relatively long reign, Munster remained under his control and his excursions into surrounding territories, particularly during the early part of his career, signalled that Uí Briain ambition was very much alive – as would be convincingly demonstrated by his descendants.