Clann Ruaidhrí was a leading medieval clan in the Hebrides and the western seaboard of Scotland. The eponymous ancestor of the family was Ruaidhrí mac Raghnaill, a principal member of Clann Somhairle in the thirteenth century. Members of Clann Ruaidhrí were factors in both the histories of the Kingdom of the Isles and the Kingdom of Scotland in the thirteenth- and fourteenth centuries. The family appears to have held power in Kintyre in the thirteenth century. By the fourteenth century, the family controlled an extensive provincial lordship stretching along the north-western Scottish coast and into the Hebrides. As a leading force in the Kingdom of the Isles, the family fiercely opposed Scottish authority. With the collapse of Norwegian hegemony in the region, the family nimbly integrated itself into the Kingdom of Scotland.

Members of Clann Ruaidhrí distinguished themselves in the First War of Scottish Independence, opposing adherents of both the English and Scottish Crowns. Like other branches of Clann Somhairle, Clann Ruaidhrí was a noted exporter of gallowglass warriors into Ireland. The mid fourteenth century saw the diminishment of the family in both Scotland and Ireland. The last Irish gallowglass captain appears on record in 1342, whilst the last great chief of the family was assassinated in 1346. Following the latter's death, the Clann Ruaidhrí lordship passed into the possession of the chief of Clann Domhnaill, a distant Clann Somhairle kinsman, and thereby formed a significant part of the Clann Domhnaill Lordship of the Isles. There is reason to suspect that the lines of the family may have continued on, albeit in a much diminished capacity, with one apparent member holding power as late as the early fifteenth century.

Clann Ruaidhrí was a branch of Clann Somhairle. Other branches of this overarching kindred included Clann Dubhghaill and Clann Domhnaill. The eponymous ancestor of Clann Ruaidhrí was Ruaidhrí mac Raghnaill, Lord of Argyll, a paternal grandson of Somhairle mac Giolla Brighde, King of the Isles, the common ancestor of Clann Somhairle. Ruaidhrí's father, Raghnall mac Somhairle, was also the father of Domhnall mac Raghnaill, eponym of Clann Domhnaill. Somhairle's abrupt death in battle in 1164, coupled with the vast territorial extent of his offspring, may account for the rapid fracturing of Clann Somhairle into rival segments.

Ruaidhrí was probably the senior of Raghnall's sons. Whilst Ruaidhrí is likely one of the unnamed sons of Raghnall who is recorded to have campaigned with Thomas fitz Roland, Earl of Atholl against the Irish in 1211/1212, he is certainly reported to have assisted Thomas in the ravaging of Derry and surrounding countryside in 1213/1214. On one hand, these seaborne operations may have been undertaken in the context of supporting the Irish interests of Rǫgnvaldr Guðrøðarson, King of the Isles, who seems to have been under pressure at about this period. It is also possible that the raids were conducted in specific regard to the interests of both the Scottish and English Crowns, and particularly aimed at limiting Irish support of the Meic Uilleim, a discontented rival branch of the Scottish royal family.

By the second decade of the thirteenth century, Ruaidhrí may have been the principal member of Clann Somhairle, and appears to have overseen an important marital alliance with the two foremost members of the Crovan dynasty. For example, Rǫgnvaldr, and his younger half-brother Óláfr, are recorded to have married the daughters of an unidentified nobleman from Kintyre, and the fact that Ruaidhrí and his father are known to have been styled Lord of Kintyre suggests that either man could have been the father of the brides. The marital alliance appears to have been orchestrated in an effort to patch up relations between Clann Somhairle and the Crovan dynasty, neighbouring kindreds who had bitterly contested the kingship of the Isles for about sixty years. It is possible that Rǫgnvaldr's kingship was formally recognised by Ruaidhrí, who thereby established himself as a leading magnate within a reunified Kingdom of the Isles. Since the majority of Ruaidhrí's territories appear to have been mainland possessions, it is very likely that the Scottish Crown regarded this reunification as a threat to its own claims of overlordship of Argyll. Apprehension of this rejuvenated island realm may have been one of the factors that led to Ruaidhrí's apparent expulsion from Kintyre by the royal forces of Alexander II, King of Scotland in the early 1220s.

There is reason to suspect that Ruaidhrí is identical to the Clann Somhairle dynast, named in surviving sources only as Mac Somhairle, who was killed whilst resisting an English invasion of Tír Chonaill in 1247. Immediately after this event, Clann Ruaidhrí was certainly represented by Ruaidhrí's son, Dubhghall. Under the later, the kindred certainly involved itself against the English in Ireland. In 1258, Dubhghall is recorded to have clashed with and killed Jordan d'Exeter, the English Sheriff of Connacht. The following year, Aodh na nGall Ó Conchobhair, son of the Uí Conchobhair King of Connacht, is recorded to have married a daughter of Dubhghall, and to have received a tocher of one hundred and sixty gallowglass warriors commanded by Dubhghall's younger brother, Ailéan. Ailéan is, therefore, one of the earliest known warriors of this type. Along with Dubhghall's naval operations of the previous year, the marital alliance between the Uí Conchobhair and Clann Ruaidhrí appears to have formed part of a carefully coordinated plan to tackle English power in the north west of Ireland. Nevertheless, Aodh na nGall and his allies were utterly crushed in battle in 1260, a conflict in which the Clann Ruaidhrí gallowglasses may well have fought.

The year after Mac Somhairle's death in 1247, Dubhghall and the chief of Clann Dubhghaill, Eóghan Mac Dubhghaill, both travelled to Norway seeking the kingship of the northern Suðreyjar from Hákon Hákonarson, King of Norway. Although the entirety of the Suðreyjar roughly encompassed the Hebrides and Mann, the precise jurisdiction which Dubhghall and Eóghan competed for is uncertain. For example, the northern Hebridean islands of Lewis and Harris and Skye appear to have been held by the Crovan dynasty, then represented by the reigning Haraldr Óláfsson, King of the Isles. Whatever the case, it is possible that the events of 1247 and 1248 were related, and that Dubhghall and Eóghan sought to succeed Mac Somhairle's position in the Isles.

It was only after the unexpected death of Haraldr in 1248 that Hákon sent Eóghan west over sea to temporarily take up the kingship of the Isles on his behalf. Eóghan, however, was not only a Norwegian dependant in the Isles, but an eminent Scottish magnate on the mainland. Although the Scottish Crown appears to have attempted to purchase the Isles earlier that decade, Eóghan's acceptance of Hákon's commission led Alexander II to unleash an invasion of Argyll in the summer of 1249, directed at the very heart of the Clann Dubhghaill lordship. The unfolding crisis only ended with the Scottish king's untimely death in July 1249. Eóghan appears to have been utterly dispossessed by the Scots a result of their invasion. In fact, his apparent displacement could well have upended the hierarchy of Clann Somhairle. For instance, within the very year that Eóghan was forced from Argyll by the Scots, Dubhghall is recorded to have "took kingship" in the Isles. This record could reveal that Dubhghall assumed the kingship from a severely weakened Eóghan.