O'Connor Donn (Ó Conchobair Donn), Aodh Óg (d. 1490), lord of the O'Connor Donns, was the second son of Aodh O'Connor Donn (qv) (d. 1461), lord of the O'Connor Donns. Nothing is known of his early years. On the death of his father on 15 May 1461, the succession passed to his brother Feidhlimidh O'Connor Donn (qv) (d. 1474), who faced considerable opposition from his kinsmen, principally the tánaiste, Ruaidhrí O'Connor Donn (qv) (d. 1473), the elder brother of Aodh Óg; although the annals are silent on the matter it is likely that Aodh sided with Ruaidhrí in the dispute. Ruaidhrí was killed in 1473 by the MacWilliam Burkes at Kilbree in the Mayo barony of Burrishoole, leaving Feidhlimidh to reign unchallenged. When he too was killed, by the O'Kellys of Uí Mháine in 1474, Aodh Óg's minor status was further confirmed by the nomination of Donnchadh Dubshúileach and Tadhg O'Connor Donn as rival leaders. Feidhlimidh's son Eóghan Caoch O'Connor Donn (qv) (d. 1485) seized the leadership in 1478, whether with Aodh Óg's approval is unknown. But Eóghan Caoch reigned only for seven years, dying after a long illness in 1485, and overlordship passed finally to Aodh Óg.
By 1487 Aodh Óg was struggling to assert his authority over his kinsmen and asked Uilleag Burke (qv) of Clanricard (d. 1509) for help. Burke led his army against the O'Connor Ruadhs and the O'Kellys of Uí Mhaine and eventually Aodh Óg and the O'Connor Ruadhs made peace: Aodh Óg and his kinsmen ceded to their rivals half the townland of Ballyclare and five townlands of Ceann Coradh in the O'Beirne lordship in east Roscommon. In 1489 Aodh Óg's position was rapidly declining, his difficulties compounded by the opportunism of the O'Connor Ruadhs and the MacDermotts, who burned his town of Ballintober; many of his vassals responded to this latest humiliation by switching their allegiance to the now dominant Feidhlimidh Fionn O'Connor Ruadh (qv) (d. 1490). Aodh Óg died soon afterwards, probably in 1490; he was succeeded by his nephew Toirdhealbhach Óg son of Ruaidhrí O'Connor Donn (d. 1503).