O'Donnell (Ó Domhnaill), Aodh Ruadh (1429–1505), king of Tír Conaill, was seemingly third son of Niall Garbh O'Donnell (qv), king of Tír Conaill, and Fionnuala, daughter of An Calbach O'Connor Faly (qv), lord of Offaly, and Mairghréag O'Carroll (qv). According to annalistic sources, Aodh Ruadh was born in 1429; apart from this, nothing survives to tell us of his youth. After the capture of his father in late 1434, Aodh Ruadh's uncle Neachtan O'Donnell (qv) ruled over Tír Conaill. Indeed, Neachtan's position was confirmed by Niall Garbh's death in captivity (1439). In the 1440s Niall Garbh's sons allied themselves to Énrí O'Neill (qv) of Tír Eóghain, leading to their banishment from Tír Conaill. As a result Aodh Ruadh and his elder brother, Domhnall O'Donnell (Ó Domhnaill) (d. 1456), were encouraged by Énrí to kill Neachtan in 1452. However, Neachtan's sons refused to give up and civil war followed. In 1454 Domhnall was seemingly installed by Énrí as king of Tír Conaill against Neachtan's son, Ruaidhrí O'Donnell (qv). Luck, though, was on the side of Aodh Ruadh and Domhnall, for at the siege of Inis (1454) the latter fortuitously killed Ruaidhrí. This enabled them to strengthen their grip on Tír Conaill; but their tenure was brief, as Toirdhealbhach Cairbreach O'Donnell (qv), Ruaidhrí's brother, avenged his death on 18 May 1456, killing Domhnall. Part of Toirdhealbhach Cairbreach's success can be explained by the fact that Énrí O'Neill had switched sides. As for Aodh Ruadh, he was captured and given to Énrí as a hostage. By 1460, however, Énrí judged that Toirdhealbhach Cairbreach was expendable as an ally. As a result he released Aodh Ruadh and allowed him to raise an army. At the battle of Ceann Maghair (1461) Aodh Ruadh decisively defeated Toirdhealbhach Cairbreach, capturing his rival. To cement his grip on the kingship and to make an example, he maimed Toirdhealbhach by removing his foot and hand. By 1464 he had fallen out with Énrí, but he proved durable and steadily built himself up as a viable alternative to the regional dominance of the O'Neills. In particular, he began to interfere actively in Connacht, and the growth of his influence is evidenced by his marriage to Fionnuala, daughter of Conchobhar O'Brien (qv) of Thomond. Throughout the 1470s he struggled with Énrí O'Neill for regional supremacy in Connacht–Ulster, and by 1480 there were signs that Aodh Ruadh was gradually gaining the upper hand. His most notable achievement of this period was his two-year confinement of Énrí's son Conn (1481–3). Unsurprisingly, Conn hid his shame by immediately beginning a new war on his release in 1483. By 1489 Aodh Ruadh had reached the peak of his career, demonstrating his military might both in east Ulster and in Connacht. Thereafter his reign was marred by the feuds of his overly competitive sons.
After his return from the court of James VI of Scotland in 1494, Aodh Ruadh failed to take Sligo castle from the O'Connors of Sligo. It is also clear that his choice of his son Conn as his successor was hotly disputed by his other sons. In June 1497 Aodh Ruadh resigned in favour of Conn, but the latter's death (19 October) at the hands of the O'Neills forced him back to the forefront of regional politics. He then offered the kingship to his younger son, Aodh Dubh (qv), who refused it and instead proposed that they should rule jointly, a solution that greatly pleased his father. Although still plagued by discontented siblings, Aodh Ruadh and Aodh Dubh were easily a match for them, and despite old age Aodh Ruadh remained an active and vigorous ruler, allying with Gerald FitzGerald (qv), 8th earl of Kildare. Indeed, he displayed his valour at the age of 73 at the battle of Knockdoe (19 August 1504), fighting for Kildare against the Burkes and O'Briens. This remarkable ruler of Tír Conaill and much of north-western Ireland died 11 July 1505, and was succeeded by Aodh Dubh.