Ímar in the context of "Siege of Dumbarton"

Ivar the Boneless (Old Norse: Ívarr hinn Beinlausi [ˈiːˌwɑrː ˈhinː ˈbɛinˌlɔuse]; died c. 873), also known as Ivar Ragnarsson, was a Viking leader who led invasions into England and Ireland. According to the Tale of Ragnarr Loðbrók, he was the son of Aslaug and her husband Ragnar Loðbrok, and was the brother of Björn Ironside, Halvdan (or Hvitserk), Sigurd Snake-in-the-Eye, and Ragnvald. However, it is not known whether this is historically accurate. Ivar is sometimes regarded as the same person as Ímar, a Viking king of Dublin between 870 and 873.

It is unclear why Ivar acquired the nickname "boneless". Some sagas claim that he was born with a skeletal condition which left him unable to walk, while others suggest that he was merely impotent.

Olaf Guthfrithson or Anlaf Guthfrithson (Old Norse: Óláfr Guðrøðsson [ˈoːˌlɑːvz̠ ˈɡuðˌrøðsˌson]; Old English: Ánláf; Old Irish: Amlaíb mac Gofraid; died 941) was a Hiberno-Scandinavian (Irish-Viking) leader who ruled Dublin and Viking Northumbria in the 10th century. He was the son of Gofraid ua Ímair and great-grandson of Ímar, making him one of the Uí Ímair. Olaf succeeded his father as King of Dublin in 934 and succeeded in establishing dominance over the Vikings of Limerick when he captured their king, Amlaíb Cenncairech, in 937. 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. The forces of Olaf and Constantine were defeated by the English led by Æthelstan at the Battle of Brunanburh in 937.

Olaf returned to Ireland in 938 but after Æthelstan's death the following year Olaf left for York where he was quickly able to establish himself as king, with his brother Blácaire mac Gofraid being left to rule in Dublin. Olaf and Æthelstan's successor Edmund met in 939 at Leicester where they came to an agreement regarding the division of England between them. This agreement proved short-lived, however, and within a few years Vikings had occupied the Five Boroughs of Derby, Leicester, Lincoln, Nottingham and Stamford. Olaf died in 941 and was succeeded in Northumbria by his cousin Olaf Cuaran. At the time of his death, the Irish annals title him "king of Danes" and "king of the Fair Foreigners and the Dark Foreigners".