O'Neill (Ó Néill), Enrí (c.1400–1489), lord of Tír Eoghain, was eldest son of Eóghan O'Neill (qv), king of Tír Eóghain, and Caitríona, daughter of Ardghal MacMahon (qv). The first reference to Enrí comes in 1431, when he was captured by Neachtan O'Donnell (qv), brother to the king of Tír Conaill. Throughout the 1430s he proved himself a commander of exceptional skill, and was to the forefront of his father's campaigns against the O'Donnells, O'Neill rivals, and the Anglo-Irish families of MacQuillin and Savage. By 1442 Enrí and his father had established their dominance over Tír Conaill by their defeat of Neachtan O'Donnell. However, they were markedly less successful in their attempts to conquer the O'Neills of Clann Aodha Buidhe. With the consent of his father and dynasty, Enrí demonstrated his power by confirming an indenture with Richard (qv), duke of York (also earl of Ulster and the king's lieutenant), at Drogheda (27 August 1449).
In 1452 Enrí had Neachtan O'Donnell murdered, and deserted his wife Gormflaith MacMurrough (d. 1465) in favour of O'Donnell's widow, daughter of MacWilliam Burke. This act enraged Gormflaith's uncle James Butler (qv), 4th earl of Ormond, who brought an army northwards and compelled Enrí to put away his new wife and take back Gormflaith. In July 1455 Enrí was inaugurated as king of Tír Eóghain, having deposed his aged father, an act that was confirmed by Archbishop John Mey (qv) of Armagh the following month. From his inauguration to his death, Enrí desisted from attacking the colonists, and his political craft ensured that O'Neill power grew unhindered by royal intervention in Ulster. This was achieved by the development of good relations with the English crown. This fruitful relationship resulted in his acceptance of a gift of scarlet livery and a gold chain from Edward IV, and he was called the ‘king's friend’ in 1471.
Enrí did, however, campaign throughout Ulster against traditional enemies, achieving the O'Neill dream of provincial dominance. Ironically, he was publicly thanked for his good services by the parliament of 1480. He also recognised the impending rise of the house of Kildare, and shrewdly married his son Conn (qv) to Lady Eleanor, daughter of Thomas FitzGerald (qv), 7th earl of Kildare. Mindful of his father's fate, he abdicated in favour of Conn in 1483, dying eventually 15 June 1489. Enrí’s political legacy was O'Neill provincial hegemony. It was an achievement his successors could not maintain.