The Macdonalds of Sleat are a branch of Clan Donald — one of the largest Scottish clans. The eponymous ancestor of Clan Donald is Domhnall, son of Raghnall, son of Somhairle. Traditional Clan Donald genealogies, created in the later Middle Ages, give the clan a descent from various legendary Irish figures. Modern historians, however, distrust these traditional genealogies, and consider Somhairle, son of Gille Brighde to be earliest ancestor for whom there is secure historical evidence. Somhairle, himself, was a 12th-century leader, styled "king of the isles" and "king of Argyll"; yet there is no reliable account for his rise to power. The Macdonalds of Sleat descend from Domhnall's son, Aonghas Mór; and then from his son, Aonghas Óg. Angus Óg's son, Eoin, was the first Lord of the Isles. Eoin I's first marriage was to Áine, heiress of "Clann Ruaidhrí" (which was founded by Ruaidhrí, elder brother to Domhnall, founder of Clan Donald). Eoin I later divorced Áine and married Margaret, daughter of Robert II. The children from Eoin I's first marriage were then passed over in the main succession of the chiefship of Clan Donald and later Macdonald lords of the isles, in favour of those from his second marriage. Eoin I was succeeded by his son, Domhnall of Islay; who was in turn succeeded by his son, Alasdair of Islay. The Macdonalds of Sleat descend from Ùisdean, bastard son of Alasdair of Islay and the daughter of Ó Beólláin (O'Beolan), Abbot of Applecross. From Ùisdean, the Macdonalds of Sleat are also known in Gaelic as "Clann Ùisdein" ("the children of Ùisdein"). The first record of Ùisdean occur in the traditional histories of the shenachie MacVurich and Hugh Macdonald. According to the Sleat shenachie, Ùisdean, along with several young gentlemen from the Western Isles went on a raiding expedition to Orkney. The tradition runs that the Western Islesmen were victorious in their conflict with the Northern Islesmen, and that the Earl of Orkney was also slain. Ùisdean is then said to have ravaged Orkney, and carried off much loot.