Clann Ruaidhrí was a leading mediaeval kindred 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 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 (died 1247), a paternal grandson of Somhairle mac Giolla Brighde, King of the Isles (died 1164), the common ancestor of Clann Somhairle. Ruaidhrí's father, Raghnall mac Somhairle (died 1191/1192–c.1210/1227), 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.