MacMahon (Mac Mathghamhna), Aodh Ruadh (d. 1453), king of Oriel, was eldest son of Ruaidhrí MacMahon, king of Oriel; nothing is known of his mother. On his father's death (1446), Aodh Ruadh was appointed successor by Eóghan O'Neill (qv) (d. 1456). In response to the elevation of Fearghal O'Reilly (qv) (d. 1459) to the kingship of Breifne by his supporters and the Anglo-Irish, Aodh Ruadh and O'Neill made Seaán O'Reilly (qv) (d. 1460) their king of Breifne. By 1452 Aodh Ruadh had fallen out with O'Neill and was allied with the Anglo-Irish. That year they foiled O'Neill's raid on the Anglo-Irish of the Fews, inflicting heavy losses on his gallowglass. This enraged O'Neill, but the wise counsel of his son Énrí O'Neill (qv) prevented the outbreak of war. Relieved by this unexpected respite, Aodh Ruadh made the most of it by repairing northward and submitting before O'Neill. He died on 31 March 1453, and was succeeded by his cousin, Feidhlimidh MacMahon. During the reign of Feidhlimidh, Aodh Ruadh's brothers and sons seem to have faithfully followed him, but they continued to expand their own territory at the expense of their Maguire neighbours.
In 1466 Aodh Ruadh's son, Aodh Óg MacMahon (Mac Mathghamhna) (d. 1496), appears for the first time in an annalistic reference, recording his capture during Feidhlimidh's defeat by the Meath Anglo-Irish. During the same year Feidhlimidh died and was succeeded by the short reign of Eóghan son of Ruaidhrí MacMahon. On the latter's death (1467) he was succeeded by his brother Réamonn (qv). It is uncertain when Aodh Óg was released from captivity, but by the middle of the 1470s he was a major power within MacMahon dynastic politics. Perhaps as a result of his imprisonment, he cultivated relations with the Anglo-Irish. With their aid he routed and captured Réamonn (1475), and ensured the permanent removal of Réamonn's threat by delivering him to the Anglo-Irish, who imprisoned him till his death. In the interim Aodh Óg waged an unceasing war against the sons of Réamonn, forcing them into exile in O'Reilly's kingdom of Breifne. Thus when Réamonn died in Drogheda jail (November 1484), Aodh Óg brushed aside his remaining competitors and ensured his smooth inauguration as king of Oriel in 1485. In the next year he exercised his new muscle by rounding on his former colonist allies, burning twenty-eight of their settlements.
In spite of Aodh Óg's dominance, the sons of Réamonn recovered their former military strength. To prevent the erosion of his hard-won position, Aodh Óg allied himself to the O'Neills. This alliance was offset by the rise of Aodh Ruadh O'Donnell (qv), king of Tír Conaill, and resulted in their near rout by his forces in Connacht (1493). None the less, Aodh Óg readjusted himself, allying with the O'Reillys to defeat the Anglo-Irish in 1494. The next year he forced the submission of the sons of Réamonn before dispatching his son Giolla Pádraig to raid Fermanagh. This was the height of Aodh Óg's power; 1496 was to be disastrous for him. It began well enough with Giolla Pádraig's elimination of several dynastic rivals during his burning of Monaghan (11 January). Retribution was both swift and terrible. Led by Brian MacMahon (qv), son of Réamonn, all the MacMahons opposed to Aodh Óg's rule scorched his lands a week later. Clearly the sons of Réamonn sensed weakness, burning Aodh Óg's chief house to the ground at the beginning of the summer. The killing of Giolla Pádraig (27 May) was enough to persuade Aodh Óg to seek refuge with the O'Reillys. Now Brian son of Réamonn sensed victory and stepped into the political void, occupying Aodh Óg's territory. However, Aodh Óg was still at large and dangerous. Knowing of his enemy's resourcefulness, Brian son of Réamonn asked Aodh Ruadh O'Donnell to join his hunt. Together they entered Breifne, defeating Aodh Óg and the O'Reillys. The fugitive was finally caught and blinded, dying in consequence before the end of the year. However, the success of Réamonn's sons was ephemeral, as Brian son of Réamonn fell in battle (5 July 1497), clearing the path to the kingship for Aodh Óg's nephew Rossa (d. 1513) son of Maghnus MacMahon. The feud continued unabated. But Rossa's victory at the battle of Slieve Beagh (1500) secured his kingship from their ambitions and allowed him to build up regional power to his death in 1513.