Muirchertach na Cochall Craicinin (d. 943), son of Niall Glúndub (qv) and king of Ailech, belonged to the Northern Uí Néill dynasty of Cenél nÉogain. His father was king of Tara; his mother was either Aillinn. daughter of Ainbith son of Áed, king of Úlaid, or Lann, daughter of Eochaid king of Dál Riata. He had at least two brothers or half-brothers, Conaing and Máel-Ciaráin. Muirchertach in turn married Flann(a), daughter of the Clann Cholmáin king of Tara, Donnchad Donn (qv) son of Flann Sinna (qv), and Dubdara daughter of Cellach king of Osraige. He had four sons, Domnall (Domnall Ua Néill (qv)), Flaithbertach, Murchad, and Flann.
When Muirchertach's father was slain in battle with the Norsemen of Dublin (919), the paramount Uí Néill kingship was claimed by Donnchad Donn of Clann Cholmáin, while the kingship of Ailech passed to a first cousin, Fergal son of Domnall. Muirchertach himself, however, rose to prominence shortly afterwards. In 921, after the Dublin Norse led by Gofraid, grandson of Ímar (qv), had plundered Armagh, he defeated a section of the invading force that had pressed further north. Although his cousin remained king of Ailech till his death (938), Muirchertach achieved a distinguished military reputation fighting the Norsemen of Dublin and enforcing the authority of his dynasty within northern Ireland. Indeed his success in this respect led to his being celebrated in later Uí Néill political propaganda as Muirchertach na Cochall Craicinn (of the leather cloaks) – from the mantles allegedly worn by his soldiers. A Norse fleet from Loch Cuan, under Alpthann son of Gofraid, landed at Linn Duachail (Annagassan, Co. Louth) on 4 September 926. Muirchertach blockaded the Norsemen, and on 28 December he attacked them at Snám Aignech on the shore of Strangford Lough, slaying their leader, and driving them back to Annagassan.
Muirchertach's efforts to enforce Cenél nÉogain dominance in the north of the province included the slaying of a king of the Cianachta in 927. That year, he challenged the right of the king of Tara, Donnchad son of Flann, to celebrate the Óenach Tailten (fair of Tailtiu; Teltown, Co. Meath). Meanwhile, the uneasy peace that had existed between Clann Cholmáin and Cenél nÉogain was threatened when, in 929, Donnchad son of Flann led an expedition to Liathdruim. It may have been at this stage that Muirchertach entered into a marriage alliance with the Southern Uí Néill; certainly, a modus vivendi was reached between the two sides. However, 933 proved a difficult year for Muirchertach: he was defeated, with the loss of several retainers, by his cousin, Fergal son of Domnall.
It was not till after the death of Fergal (938) that Muirchertach was able to take the kingship of Ailech; his own brother, Conaing, had died a year earlier. This elevation in status made him an important player in interprovincial politics. Shortly after his accession, he marched against his father-in-law Donnchad, but the two made terms and joined forces to plunder the hinterland of the Norse kingdom of Dublin. Notwithstanding a setback the following year, when he was captured in a Norse raid on Ailech and forced to purchase his freedom, his political influence continued to expand. He joined with Donnchad again in 940; the two led an expedition to Leinster and Munster, taking hostages from both provinces.
Around that time, Muirchertach's wife Flann(a) died, but he remarried early in 941. That same year, he led a naval expedition to the Hebrides and brought back rich booty. During his absence the Éoganachta attacked his allies, the Déisi. His retaliation on this occasion was enlarged on in a later poem on his ‘circuit of Ireland’ ascribed to the poet Cormacán (d. 948) son of Máel-Brigte, who is alleged to have accompanied his forces. Nonetheless, his march through Mide, Uí Fhailge, Osraige, and Déisi and his taking of hostages on behalf of Donnchad was probably historical; the high point of the expedition was the capture of the Éoganacht overking of Munster, Cellachán Caisil (qv), whom he brought back as a captive to Mide.
Selected achievements of Muirchertach's career, presumably also enlarged, are commemorated in a poem of Flann Manistrech (qv) preserved in the Book of Leinster. Seemingly at the height of his power, on 26 February 943 Muirchertach was defeated and slain in the territory of Fir Rois (south of Dundalk) by a raiding force of Dublin Norsemen under Blacair (qv) son of Gofraid. Styled in the annals as rígdamna Hérend (eligible for the high-kingship of Ireland), Muirchertach was succeeded in the kingship of Ailech by his son Domnall from whom later kings of the Uí Néill descended.