That same year he allied with Constantine II of Scotland in an attempt to reclaim the Kingdom of Northumbria which his father had ruled briefly in 927.

This agreement proved short-lived, however, and within a few years Vikings had occupied the Five Boroughs of Derby, Leicester, Lincoln, Nottingham and Stamford.

[6][2] Olaf is described as "Lord of the Foreigners" by the Annals of the Four Masters in 937,[8] at which time he went to Lough Ree and captured Amlaíb Cenncairech, King of Limerick, and his troops after breaking their boats.

[10] The annals record Olaf's return to Ireland in 938 as well as a raid he carried out that year on Kilcullen in modern-day County Kildare, where he is said to have taken a thousand prisoners.

[6] Æthelstan died in October 939 and very soon afterwards Olaf left for York where he was able to quickly establish himself as king of Northumbria.

[14][15] Symeon of Durham's Historia Regum records that Olaf and the new English king Edmund met at Leicester in 939 and came to an agreement on dividing England between the two of them.

[16] This peace was short-lived and within a few years of the agreement the Vikings had seized the Five Boroughs of Derby, Leicester, Lincoln, Nottingham and Stamford.

[nb 3][17] In 941 the Chronicle of Melrose records that Olaf raided an ancient Anglian church at Tyninghame in what is now the East Lothian and at the time was a part of Northumbria.

Grave goods including a belt similar to others known to have been worn in Viking-age Ireland indicate that the skeleton belonged to a high-status individual.

Woolf has also suggested that "there is a strong likelihood that the king’s followers hoped that by burying him in the saint’s cemetery he might have benefitted from some sort of post-mortem penance".

[27] Ímar, possibly identical to Ivar the Boneless, was the founder of the Uí Ímair and was one of the earliest kings of Dublin in the mid-ninth century.

[14][30] John of Worcester, writing in the twelfth century, claimed that Olaf had married a daughter of Constantine II of Scotland prior to 937, but this evidence is considered unreliable.