Thorfinn (1009-1065), known as Thorfinn the Mighty, was the youngest son of Earl Sigurd of Orkney and his successor as Earl of Orkney and Shetland.
He inherited his Earldom as a babe in arms when his father was killed at the battle of Clontarf in 1014. Thorfinn’s minority was a time of disruption, and allowed Harold the Black to reclaim Sodor and Man. By 1032 he had set about bringing his earldom into order again. Further he extended his “empire” to include not only the Hebrides, Dublin, Sodor and Man, but western and northern regions of Scotland as well.
Thorfinn sized control of Sodor and Man in 1034 when he drove out Harold to exile in Iceland and killed his son. He appointed a puppet King named Fignall to rule in Harold's place, though Fignall acted like a tyrant. By 1063, Thorfinn's power was waning and Harold's second son, Godred Crovan, began preparing to claim his father's Kingdom.
His sons Erland and Paul ruled the earldom jointly after his death in 1065, but were unable to prevent considerable loss of territory at the hands of adventurers such as Godred Crovan, who managed to reclaim Sodor by 1067, and others. He was considered to be the greatest of the Norse Earls.
- Thorfinn the Mighty (Thorfinn Sigurdsson) is a real historic figure who was Earl of Orkney between 1016 and 1065.