Somerled (a.k.a. Sumarlidhi Höld) was born in about 1113 (sources differ) and either in Morvern or in northern Ireland (ditto). His father was Gillebride Mac Gille Adomnan, a descendant of a noble Gaelic family who were probably an offshoot of the House of Alpin at the time Kenneth I combined Dalriada with Pictavia. Somerled's mother was of Norse descent. The wider picture in Scotland at the time is set out in our Historical Timeline.
Somerled's grandfather, Gilledomman of the Isles, had been defeated by the Norse and exiled to Ireland. When he was a child, Somerled's more immediate family was also expelled from their home and sent to Ireland. His father Gillebride raised an army of 500 and returned to Morvern to regain their lands; but was beaten off and killed.
Much of Somerled's youth was spent on the margins of life in his native land. But some time around 1135 he became the leader of a rebellion against the Norse control. He successfully cleared Morvern, Lochaber and the northern part of Argyll from Norse influence and became known as Thane of Argyll: possibly with the formal endorsement of David I of Scotland who would have been grateful to see the Norse tide turned back in at least one part of Scotland.
In 1140, Somerled extended his area of influence by marrying Ragnhild, daughter of Olaf the Red (Olaf I The Red Godredson), the Norse King of Man, whose territory included the Hebrides. They had three sons, Dughall, Ragnald, and Aonghus. Somerled also had one son by a previous marriage: Gillecallum. Shortly afterwards Somerled helped suppress an uprising against Olaf the Red.
In 1143 Olaf the Red was murdered by the sons of his brother Harold but was succeeded as King of Man by his son (and Somerled's brother in law) Ochraidh Godred II the Black Olafson, or Godfrey the Black. Godfrey ruled with a heavy hand, and was deeply unpopular. In 1155 there was an uprising against Godfrey, and this time Somerled backed it.
Somerled's involvement proved decisive. Using a fleet of galleys fitted with rudders, the latest in naval technology, he defeated Godfrey at the Battle of Epiphany (probably off Islay) on 5-6 January 1156 and declared himself Ri Innse Gall or King of the Isles. What Somerled had achieved was to introduce a "third force" into the long-standing conflict between the Kings of Scotland and the Kings of Norway over the ownership of the Hebrides. While the title Ri Innse Gall dated back centuries before Olaf the Red, all its holders up to Godfrey the Black owed allegiance to the King of Norway. In contrast, Somerled's Kingdom of the Isles was not a subservient kingdom to the Kingdom of Norway, it was a separate kingdom, independent of both Norway and Scotland.
The newly powerful Somerled was seen as a serious threat by King Malcolm IV of Scotland, and in 1160 the two met in indecisive battle in Argyll. After an uneasy peace, conflict was resumed in early 1164. Somerled landed an army of 15,000 men from 164 galleys at Greenock. He intended to capture Renfrew, but somewhere near Inchinnan (close to the site of today's Glasgow Airport), Somerled was intercepted by forces under Walter Fitzalan, High Steward of Scotland. Somerled betrayed and killed, allegedly by a nephew in the pay of Malcolm IV. His army returned to their galleys and departed without engaging in a full scale battle. Accounts differ as to whether Somerled was buried on Iona or at Saddell Abbey.
Somerled is credited with breaking the stranglehold of the Norse on western Scotland and the Isles. There is a certain irony in this as he was himself Norse on his mother's side (and possibly in part on his father's side according to DNA studies); and he had married into the family of Olaf the Red. The independent kingdom he had briefly created was not to outlive him, but Somerled had changed things for good.
After his death, Somerled's Kingdom of the Isles was divided amongst his three sons from his marriage to Ragnhild. The descendants of Aonghus went on to form the Clan McRuari or McRory; the descendants of Dughall went on to form the Clan MacDougall; and the descendants of Ragnald's son Donald Mor McRanald would become the Clan Donald, who went on to found the Lordship of the Isles. Widespread DNA studies suggest that as many as 500,000 people living today are descended from Somerled: this is a number only bettered by Genghis Khan who, again according to DNA studies, is estimated to be the ancestor of 16 million people alive today.