Magnus's grandparents, Thorfinn the Mighty, Jarl of Orkney and his wife Ingibiorg Finnsdottir, had two sons, Erlend and Paul, who were twins.

[3] Of the three texts Vigfusson (1887) considers the shorter saga to be the "best authority", noting that it is "of ecclesiastical origin" and "composed with pious intent" rather than to "satisfy a love of good tales".

[4] As is commonly the case for medieval saints' tales a short book of miracles is appended to both the shorter and longer lives, although they contain somewhat different material.

There is also a surviving Latin account of Magnus's life, the Legenda de sancto Magno, and other material in the Brevarium Aberdonense of 1509/10, no doubt based on the missing Vita by the above magister Rodbert - part of which is included in the Magnús saga lengri.

[5][6] Magnus was the first son of Erlend Thorfinnsson, Earl of Orkney (who ruled jointly with his brother Paul) and Thora, a daughter of Sumarlidi Ospaksson.

[a] Paul and Erlend remained on friendly terms until their children grew to adulthood, due to the rivalry between Haakon Paulsson and Aerling Erlendsson.

[10] Haakon Paalsson went on a long journey to Scandinavia, with his cousin Ofeig, latterly staying with his kinsman, Magnus Barefoot the king of Norway.

He refused to fight in a Viking raid in Anglesey, Wales, because of his religious convictions, and instead stayed on board the ship during the Battle of Menai Straits, singing psalms.

[14] Having failed to reach an agreement, he sought help from King Eystein I of Norway, who granted him the earldom of Orkney and he ruled jointly and amicably with Haakon until 1114.

[14] Eventually however, the followers of the two earls fell out, and the sides met at the Thing (assembly) on the Orkney mainland, ready to do battle.

[15] Magnus took refuge in the island's church overnight, but the following day he was captured and offered to go into exile or prison, but an assembly of chieftains, tired of joint rule, insisted that one earl must die.

William the Old, Bishop of Orkney, warned that it was "heresy to go about with such tales" and was then struck blind at his church, but subsequently had his sight restored after praying at the grave of Magnus, not long after visiting Norway (and perhaps meeting Earl Rognvald Kolsson).

In the case of Earl Magnus it also had a political purpose in that it enabled the surviving descendants of Erlend Thorfinsson and their family to turn this death to their advantage in portraying him as a peaceful martyr.

Ultimately they succeeded in maintaining their prominent position in Orkney when Rognvald Kali Kolsson, the son of Magnus's sister Gunnhild became earl in 1136.