Of all the characters in the Orkneyinga Saga, it is perhaps Sweyn Asleifsson who has come to personify the archetypal Viking.

Christened the "Ultimate Viking" by the Orkney writer Eric Linklater, Sweyn Asleifsson comes across in the saga as a charismatic, but ruthless, character.

He was undoubtedly a fearsome warrior, although it is through cunning and tactics that he often triumphed. He was firmly entangled in the shifting politics of the 12th century Orkney Earldom and although a fierce ally, switched allegiances almost at a whim.

Sweyn used his homeland in Orkney, and properties in the Western Isles of Scotland, as bases to launch raids on the rest of the British Isles.

Concentrating on farming in the summer, Sweyn was like a number of other chieftains who went raiding whenever convenient.

According to the Orkneyinga saga:

"This was how Svein used to live. Winter he would spend at home on Gairsay, where he entertained some eighty men at his own expense. His drinking hall was so big, there was nothing in Orkney to compare with it. In the spring he had more than enough to occupy him, with a great deal of seed to sow which he saw to carefully himself. Then when that job was done, he would go off plundering in the Hebrides and in Ireland on what he called his 'spring-trip', then back home just after mid-summer, where he stayed till the cornfields had been reaped and the grain was safely in. After that he would go off raiding again, and never came back till the first month of winter was ended. This he used to call his 'autumn-trip'."
Orkneyinga Saga, chapter 105

Sweyn was born sometime before 1135, the son of Olaf Hrolfsson of Gairsay and Asleif.

His father was murdered in 1135, by Olvir Rosta, a chieftain from Sutherland, who was seeking revenge after being soundly defeated by Olaf in a sea battle off the coast of Tankerness. Olvir had launched a surprise raid on Olaf's residence in Caithness, in the north of Scotland, where he burned the house down around the warrior's head.

Later that year, during Earl Paul's Yule feasts at his Bu (hall) in Orphir, an exchange of insults between Sweyn Asleifsson and Sweyn Breastrope, a colleague of Asleifsson's father, the hot-headed young Sweyn killed Breastrope.

Outlawed by Earl Paul, Sweyn fled to the island of Egilsay, where he was despatched to the Scottish island of Tiree, on the west Coast of Scotland, by Bishop William the Old. There, Sweyn was given refuge by a chieftain referred in the saga only as Holbodi.

Back in Orkney, in 1136, Sweyn managed to kidnap Earl Paul on the island of Rousay, spiriting him away and leaving the Earldom open for Rognvald II to step in and assume control. Upon his return to Orkney, Sweyn's forfeited lands were returned by the new Earl.

In 1139, having assisted Rognvald in his efforts to gain the Earldom, Sweyn set about paying off some of his own private scores. Seeking revenge for the death of his father, Sweyn concentrated first on Olvir Rosta. To carry this out, Sweyn asked Earl Rognvald for two fully manned ships, a request the Earl granted.

Sweyn then sailed south and into the Moray Firth, intending to launch a surprise attack on Olvir Rosta's residence at Helmsdale in Northern Scotland. He landed to the south of Helmsdale and, acquiring men and guides from Earl Maddad, headed north to finally avenge his father.

Expecting the assault from the north, Olvir had concentrated his forces to the north of his lands and was therefore caught unawares. A short fight took place and Olvir's forces were routed. Olvir himself fled up the valley and escaped to the Western Isles, leaving Sweyn's men ransack the house before setting it alight and burning all the inhabitants, including Olvir's mother Frakkok.

After plundering the area, Sweyn returned to his ships and sailed back to Orkney where Earl Rognvaid "received them cordially."

In 1140, Sweyn sailing southwards again, this time to go to the aid of his comrade, Holbodi of Tiree.

While wintering at Duncansby in Caithness, a messenger had come from Holbodi asking for help against a group of Welsh marauders who had burned down his house.

Sweyn again approached Earl Rognvald asking for ships and men. His request granted, he sailed west and drove the Welshmen from Tiree, pursuing them as far as the Isle of Man. There the Welsh warriors escaped but not before killing Andres, a local chieftain.

Andres had been a man of some wealth and considerable estates. Following his death, his widow, Ingirid, was now a prize to be sought after. Sweyn asked for lngirid's hand in marriage, but she would not consent unless he he avenged her former husband's death.

Sweyn agreed and, accompanied by Holdbodi and five ships, spent the summer raiding the coasts of Wales. Failing to capture the warband that had slain Andres, Sweyn returned to the Isle of Man where he married lngirid and settled down for the winter.

The spring of 1141 saw Sweyn on the move again, but Holbodi, who was now allied to the Welsh, did not join him.

Sweyn made for Ireland, returning home in the autumn, laden with booty. In the winter Holbodi and his men attacked Sweyn's house in Man but were repelled. Now wary of the Hebrideans, Sweyn relocated to Lewis in the Western Isles, where he remained until 1143, when he returned to Orkney, and his family seat in Gairsay.

During Sweyn's time in the Western Isles, the Earl of Orkney, Rognvald, had become friendly with a man called Thorbjorn Klerk. Thorbjorn was one was of the men who had stood with Olvir when Sweyn had attacked his estate some years previously.

Rognvald sailed to Gairsay and succeeded in reconciling Sweyn and Thorbjorn. And for a time all was well between the two men.

But Holbodi's treachery was not forgotten and Sweyn once again approached the Earl looking for men and ships. Rognvald provided five vessels, and with Thorbjorn Klerk at the helm of one of the vessels, Sweyn's fleet set sail for Tiree.

Undoubtedly sensing his doom, Holbodi fled Tiree, leaving Sweyn and his allies free to loot the island. They accrued considerable plunder and agreed that their spoils should be divided equally.

But Sweyn demanded a chief's share.

This caused unease among the other captains, and after Thorbjorn complained to Earl Rognvald, the Earl made up the captains' loss with money from his own treasury. Thorbjorn took the Earl's money but his friendship with Sweyn was ended.

During Sweyn's time in the Western Isles, he had left a man called Margad to manage his estates in Caithness. Margad, however, was somewhat tyrannical and succeeded in stirring up trouble among the people. On Sweyn's return, Margad slew a neighbouring chieftain, Hroald, in Wick, knowing well that this act would cause trouble. Sweyn gathered up sixty men - including Margad - and retired to the tower of Lambaborg and prepared for a siege.

Earl Rognvald, at the request of Hroald's son, gathered a force and laid siege to Lambaborg, demanding the surrender of Margad. Sweyn refused to give him up, so the siege continued.

As part of a daring escape plan, Sweyn instructed his men to gather all the ropes they could find and knot them together. Then, under cover of the night, Sweyn and Margad were lowered into the sea below the fortress. Swimming to safety, they escaped southwards, eventually ending up at the court of King David of Scotland.

King David managed to reconcile Earl Rognvald and Sweyn and eventually the "Ultimate Viking" returned home to Orkney.