Aonghas Óg (died 1490) was a Scottish nobleman who was the last independent Lord of the Isles. Aonghas became a rebel against both his father and the Scottish crown, in a civil clan war which would see the end of the independent Lordship of the Isles.
Aonghas was born the bastard son of John MacDonald, Earl of Ross a.k.a. (John of Islay, Lord of the Isles). In time, Aonghas would become a rebel against both his father and against the Scottish crown.
In 1476, a secret treaty that was made by Aonghas's father, John MacDonald, with King Edward IV of England was discovered by King James III of Scotland, who then stripped MacDonald of his earldom, as well as the sheriffdoms of Nairn and Inverness, and the lordships of Kintyre and Knapdale; the King however confirmed MacDonald with the remainder of his lands and the title Lord of the Isles. It appears that Aonghas, as MacDonald's heir, was not prepared to accept this settlement. Aonghas campaigned to regain Ross and the other lost dominions. At first, he may have been supported by his father, but this did not last. Aonghas married Lady Mary Campbell, daughter of Colin Campbell, 1st Earl of Argyll and Isabel Stewart.
Macdonald, his prestige in tatters, was driven from Islay by his son Aonghas. However, he managed to gather support among the MacGill'Eain ("MacLean") kindred of Duart, the MacLeoid kindred of Lewis and Harris, and the MacNeill kindred of Barra, as well as the support of the Scottish crown and John Stewart, Earl of Atholl; but, Aonghas had the important support of Domhnall Ballach and the rest of the MacDomhnaill kindred.
Aonghas gathered his forces and those of his allies against the armies of his father, and a great sea battle took place near Tobermory, the Battle of the Bloody Bay, probably in the year 1481, in which Aonghas defeated the galleys of his father's west highland allies. In the same year, another battle took place at Lagabraad, in which Aonghas defeated a royal army led by the Earl of Atholl. According to Hugh MacDonald's History of the MacDonalds, 517 of Atholl's men were slain. Aonghas followed up his victory by retaking control of Dingwall Castle and Easter Ross.
Aonghas se había beneficiado de las distracciones políticas en el sur. En 1483 esas distracciones habían terminado, y el conde de Atholl y el conde de Huntly pudieron ejercer su presencia en el norte, lo que obligó a Aonghas a retirarse hacia el oeste. Sin embargo, la rebelión del gran magnate de 1488 le dio a Aonghas otra oportunidad de avanzar hacia el este y Aonghas pudo tomar el control de Inverness.
En 1490, a Aonghas le cortaron el cuello mientras dormía. El asesino fue su arpista , Diarmaid O'Cairbre, quien llevó a cabo el acto por motivos que aún no están claros. Tras la muerte de Aonghas, la corona lanzó una nueva campaña contra el poder del Señor de las Islas, y el hijo de Aonghas, Domhnall Dubh, fue capturado por Colin Campbell, primer conde de Argyll . La muerte de Aonghas supondría el fin efectivo del Señorío independiente de las Islas. De ahora en adelante, el poder de la Casa de Estuardo y de la Corona de Escocia aumentaría considerablemente. Aonghas dejó una hija llamada Màiri, de quien descendía el bardo gaélico escocés Alasdair Mac Mhaighstir Alasdair .