Overview
Thorfinn Sigurdsson (1009?– 1065), also known as Thorfinn the Mighty (Old Norse: Þorfinnr inn riki), was an 11th-century Jarl of Orkney. He was the youngest of five sons of Jarl Sigurd Hlodvirsson and the only one resulting from Sigurd's marriage to a daughter of Malcolm II of Scotland. He ruled alone as jarl for about a third of the time that he held the title and jointly with one or more of his brothers or with his nephew Rögnvald Brusason for the remainder. Thorfinn married Ingibiorg Finnsdottir, daughter of Finn Arnesson, Jarl of Halland.
The Heimskringla of Icelandic historian Snorri Sturluson, and the anonymous compiler of the Orkneyinga Saga wrote that Thorfinn was the most powerful of all the jarls of Orkney and that he ruled substantial territories beyond the Northern Isles. A sizeable part of the latter saga's account concerns his wars with a "King of Scots" named Karl Hundason whose identity is uncertain. In his later years he went on a pilgrimage to Rome and he was instrumental in making Orkney and Shetland part of mainstream Christendom. On his death in the latter half of the 11th century he was followed as earl by his sons Paul and Erlend.
There are numerous problems associated with the chronology of Thorfinn's life and in identifying his relationships to the southern polities of the Kingdom of Alba (the precursor to modern Scotland) and the Kingdom of Moray. His diplomacy with the Norwegian court has also been interpreted in various ways. His life has been the subject of various works of historical fiction.
Sources
The sources for Thorfinn's life are almost exclusively Norse sagas, which were written down long after the time of the events in his life they record. The main sources are St Olaf's saga and the more detailed Orkneyinga Saga, which were first compiled in Iceland in the early 13th century. Much of the information the latter contains is "hard to corroborate" although it is a "generally credible" narrative in this context.
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