Aonghus Mór's first certain appearance in the historical record seems to evince his involvement in aiding native Irish kindreds against the consolidation of Anglo-Irish authority in the north-west of Ireland.

For example, Aonghus Mór was one of three members of the kindred to attended an important government council at Scone in which Alexander III's granddaughter, Margaret, was recognised as the king's rightful heir.

Following Alexander III's unexpected death two years later, Aonghus Mór and Alasdair Óg were signatories of the Turnberry Band, a pact between several Scottish and Anglo-Irish magnates.

[37][note 3] Like his Clann Somhairle kinsman, Eóghan Mac Dubhghaill, Aonghus Mór evidently named his first-born son, Alasdair Óg, after Alexander III, King of Scotland.

The episode concerning Dofnaldus concludes with him and his son successfully escaping their captors through divine intervention, and the compiler of the chronicle stating that the recorded events were provided in person by the chieftain in question.

[74] The first certain record of Aonghus Mór in contemporary sources dates to February 1256, when the English Crown commanded that he, and other unnamed men from Scotland, were not to be received in Ireland.

[79] The year before this, Aodh na nGall had been one of several leading Irishmen who relinquished their claims to the high-kingship of Ireland in favour of Brian Ó Néill, King of Tír Eoghain,[80] a man committed to combating the Anglo-Irish in Ulster.

[90] It is conceivable that the overseas support lent to the Irish insurrection was ventured in the context of not only countering the English Crown in Ireland, but of also opposing the westward extension of Scottish royal authority.

[91] In fact, another ordinance dating to just weeks before Brian's defeat—and almost certainly related to the uprising itself—directed the Anglo-Irish justiciar to arrest any Scottish subjects who were actively seeking confederacies with the Irish that might be to the king's detriment.

[103] It is conceivable that Eóghan and Dubhghall sought kingship over the same jurisdiction that Hákon had awarded to Óspakr-Hákon about a decade before—a region which could have included some or all of the islands possessed by Clann Somhairle.

[110] Although the Scottish Crown seems to have attempted to purchase the Isles earlier that decade,[111] Eóghan's acceptance of Hákon's commission partly led Alexander II to unleash an invasion of Argyll in the summer of 1249, directed at the very heart of the Clann Dubhghaill lordship.

[121] In 1262, the year after yet another failed attempt by the Scottish Crown to purchase the Hebrides, the thirteenth-century Hákonar saga Hákonarsonar reports that the Scots lashed out against the Islesmen in a particularly savage assault upon the inhabitants of Skye.

[122] Thus provoked, Hákon assembled an enormous fleet—described by the Icelandic annals as the largest force to have ever set sail from Norway[123]—to reassert Norwegian sovereignty along the north and western coast of Scotland.

[124][note 13] In July 1263, this armada disembarked from Norway, and by mid August, Hákon reaffirmed his overlordship in Shetland and Orkney, forced the submission of Caithness, and arrived in the Hebrides.

[129] The saga, and pieces of poetry embedded within it, glorifies the subsequent ravaging of Kintyre, suggesting that it was this rapaciousness that finally compelled Aonghus Mór and Murchadh to come into the king's peace.

Certainly the saga reveals that these west-coast magnates duly submitted to Hákon, swearing oaths of allegiance, surrendering hostages into his keeping, and delivering the island of Islay into his control.

The king is further said to have levied a tax of one thousand head of cattle upon the Kintyre headland, and a particular fortress[131]—most likely Dunaverty Castle[132]—is stated to have been surrendered to Hákon by an unidentified knight.

[148] Not only did Hákon fail to break Scottish power, but Alexander III seized the initiative the following year, and oversaw a series of invasions into the Isles and northern Scotland.

Recognising this dramatic shift in royal authority, Magnús Óláfsson submitted to Alexander III within the year,[149] and in so doing, symbolised the complete collapse of Norwegian sovereignty in the Isles.

[154] Evidence from the Scottish exchequer, concerning Uilleam's reception of monetary aid for commanding two hundred serjeants on behalf of the king in the Hebrides, also validates these accounts.

[155] Further evidence of a concerted campaign against Hákon's supporters is the record of Walter Stewart, Earl of Menteith assembling a royal fleet at Ayr,[156] and of Uilleam taking twenty cattle from Kintyre.

Specifically, with the conclusion of the Treaty of Perth in July, Hákon's son and successor, Magnús Hákonarson, King of Norway, formally resigned all rights to Mann and the islands on the western coast of Scotland.

He was forced to hand over his son—seemingly Alasdair Óg, his eldest son and heir—who was consequently held at Ayr as a hostage of the Scottish Crown for Aonghus Mór's good behaviour.

[163] In his submission, Aonghus Mór formally acknowledged that he would suffer disinheritance if his loyalty to the Scottish Crown was called into question again, whilst the other barons of Argyll swore to rise against him in the name of the king if such an eventuality came to pass.

[166] For instance, in 1284, Aonghus Mór attended a government council at Scone which acknowledged Alexander III's granddaughter, Margaret, as the king's rightful heir.

Forced from its Scottish homeland, Clann Suibhne evidently found a safe haven in Tír Chonaill on account of an alliance forged with Domhnall Óg.

The infighting appears to have stemmed from Alasdair Óg's marriage to an apparent member of Clann Dubhghaill, and seems to have concerned this woman's territorial claims.

[205][note 21] Days later, Alasdair Mac Dubhghaill—the Scottish Crown's leading representative in the west—was commanded to bring Aonghus Mór and two other regional landholders to do homage before the king by Easter.

[216] According to Hebridean tradition preserved by the eighteenth-century Book of Clanranald and the Sleat History, he died on Islay, with the latter source locating his burial on Iona.

[217] Alasdair Óg's undated renewal of Aonghus Mór's charter concerning the church of St Ciarán seems to be evidence that the later had been succeeded by the date of its issue.