Sigurd's tenure as earl was apparently free of the kin-strife that beset some other incumbents of this title and he was able to pursue his military ambitions over a wide area.
He also held lands in the north of mainland Scotland and in the Sudrøyar, and he may have been instrumental in the defeat of Gofraid mac Arailt, King of the Isles.
The saga tales draw attention to Sigurd's conversion to Christianity and his use of a totemic raven banner, a symbol of the Norse God Odin.
This ambiguous theme and the lack of detailed contemporary records of his life have led to a variety of interpretations of the saga material by modern scholars.
[2] Sigurd's great-grandfather, Torf-Einarr, lost the udal rights of the Orkney and Shetland farmers as part of a deal he brokered with the Norwegian crown.
[16] Sigurd's domain included not just Orkney itself but also Shetland, which formed part of the earldom and also extensive lands on mainland Scotland.
[2] Smyth (1984) notes the density of dalr placenames on Scotland's west coast and it has even been suggested that "the Dales" is a reference to Dalriada, although it is more likely that it means Caithness.
However, Orcadian influence in this part of Scotland is likely to have been temporary and on other occasions, such as during his uncle Ljot's earldom, Scottish forces had pushed north into Caithness.
Njal's Saga records an expedition that took place c. 980 in which Kari, Sigurd's bodyguard, plundered the Hebrides, Kintyre and "Bretland" (probably Strathclyde).
[18][21] The Annals of Ulster record a raid by "the Danes" on Iona on Christmas Night in which the abbot and fifteen of the elders of the monastery were slaughtered and this may have been connected with the successful conquering of the Isle of Man by Sigurd and Gilli between 985 and 989.
[21][25] Njal's Saga records a victory for Sigurd over Gofraid mac Arailt, King of the Isles with the former returning to Orkney with the spoils.
[26] Two years later Njal's Saga reports a second campaign in the southern Hebrides, Anglesey, Kintyre, Wales and a more decisive victory in Man.
Irish sources report only the death of King Gofraid in Dál Riata, an event that Thomson (2008) ascribes to Earl Gilli's Gall-Ghàidheil forces.
[33] According to the Orkneyinga saga, the Northern Isles were Christianised by King Olaf Tryggvasson in 995 when he stopped at South Walls on his way back to Norway from Dublin.
There is clearly a chronological problem with Sigurd's mother being the daughter of a king who died more than 70 years before the death of his own grandfather, Earl Thorfinn.
He concludes that "If there were no earls in Orkney before Sigurð's time it might help to explain the islands' low profile in the annals since these, for the most part, record only the deaths of great men.
[40] Although Sigurd's marriage to an unnamed daughter of Malcolm of Scotland is mentioned in the Orkneyinga Saga immediately after the death of Hunde and the earl's consequent break with Olaf Tryggvasson, Thomson (2008) views this nuptial arrangement as a joint attempt by the Orcadians and Scots to align themselves against the "common threat from Moray" rather than as a slight to Norway.
[50] The inclusion of the tale of the raven banner in the saga material may convey the idea of a revival of heathenism in Orcadian society and a reaction to Norwegian attempts to control the islands.
However, in the Orkneyinga Saga there is a vivid contrast between Sigurd's death clutching the raven banner and the later career of his son Thorfinn, who is credited with several achievements in bringing Orkney into mainstream Christendom.