Ua Canannáin, Ruaidrí (d. 950), king of Ailech, belonged to Cenél Conaill, a dynasty of the Uí Néill. He does not feature in the surviving genealogies, but his grandfather (or great-grandfather?) Canannán son of Flaithbertach was fourth in descent from Flaithbertach (qv) son of Loingsech, the last member of the dynasty before Ruaidrí's time to hold the kingship of Ailech, which implied overlordship of the Northern Uí Néill. Ruaidrí apparently had a close kinsman named Niall. In addition, Cainnech (d. 927) daughter of Canannán, who was married to the Clann Cholmáin king of Tara, Donnchad Donn (qv) son of Flann Sinna (qv), was perhaps his aunt.
Undoubtedly, Ruaidrí benefited from the fact that his reign coincided with a time of weakness for both Cenél nÉogain and Clann Cholmáin, dynasties that had dominated the politics of Uí Néill for generations. It is not clear when he emerged as ruler of Cenél Conaill; he is not mentioned in connection with the slaying (941) of the leading Cenél nÉogain dynast, Máel-ruanaid son of Flann. He had, however, apparently achieved overlordship of the north by 945, in which year he made a strong bid for the prestigious kingship of Tara, although he was very much an outside contender. This dignity was meanwhile claimed by another outsider, Congalach Cnogba (qv) son of Máel-mithig, who belonged to the dynasty of Síl nÁedo Sláine. The support of the Columban community for Ruaidrí may explain what appears to be a negative portrayal of Congalach (in the person of Congal son of Fergus) in the tenth-century Irish Life of Adomnán (qv).
In 945 Ruaidrí invaded Mide, but was repulsed by Congalach with the support of the Dublin Norsemen; his retreating forces suffered losses in Conaille (north Co. Louth). Two years later, he again struck southwards; this time he defeated Congalach and the Dubliners near Slane, the Norse forces suffering the heaviest casualties. It seems, however, that he was unable to follow up on this victory because of unrest within the north. Ruaidrí spent the next two years seeking to re-establish his authority over his northern rivals. In 949 he plundered the territory of Fir Lí (in Co. Tyrone) and slew the joint-king of Cenél nÉogain, Flaithbertach, grandson of Niall Glúndub (qv) and brother of the illustrious Domnall Ua Néill (qv).
By early 950 Ruaidrí was ready to renew his challenge for the kingship of Tara. Again, he invaded Mide and defeated Congalach. A couple of months later he returned and ravaged his rival's home-kingdom of Brega. He camped in Brega for six months so that Síl nÁedo Sláine was hard pressed. Late that year, he was attacked by the Dublin Norsemen under Amlaíb (Óláfr) Cuarán (qv). Ruaidrí and his kinsman Niall were both slain in battle at Muine Broccáin which, perhaps significantly, lay near the Columban foundation of Kells. In the Annals of Ulster, Ruaidrí is styled rígdamna Érenn, implying his eligibility to be high-king of Ireland. With his death, the Cenél Conaill challenge for the kingship of Tara collapsed.