Question: Ragnall ua Ímair was the grandson of a Viking leader that died in what year?

Context paragraphs:
Gofraid ua Ímair: Gofraid ua Ímair (Old Norse: "Guðrøðr" , died 934) was a Viking leader who ruled Dublin and briefly Viking Northumbria in the early 10th century.  He was a grandson of Ímar and a member of the Uí Ímair.  Gofraid was most probably among those Vikings expelled from Dublin in 902, whereafter he helped his kinsman Ragnall conquer Northumbria.  Another kinsman, Sitric Cáech, became ruler of Dublin around the same time.  Ragnall died in 920, and so the following year Sitric left Dublin to rule in Northumbria, and Gofraid succeeded Sitric as ruler of Dublin.  Sitric's early reign was marked by raids he conducted against the native Irish, including one at Armagh.

Ragnall ua Ímair, King of Waterford: Ragnall ua Ímair (died 1035), also known as Ragnall mac Ragnaill, was an eleventh-century King of Waterford.  He appears to have ruled as king from 1022 to 1035, the year of his death.

List of rulers of Waterford: The Vikings, who had created a longphort near Waterford in 853, finally settled and created a town in 914.  These were led by Ottir Iarla.  Ragnall ua Ímair then installed himself over them in 917, however leaving a year later to Britain, with Ottir, and presumably placing a deputy in control.  Several of the 11th century Norse kings, the descendants of Ímar (died 1000), were both allied to and vassals of the powerful O'Brien dynasty, with whom they may also have been intermarried, and who in at least one case in the 1070s (Diarmait, son of Toirrdelbach Ua Briain) exercised direct rule over the small city.

Sitric Cáech: Sitric Cáech, also known as Sitric Gále, (Old Norse: "Sigtryggr" , died 927) was a Viking leader who ruled Dublin and then Viking Northumbria in the early 10th century.  He was a grandson of Ímar and a member of the Uí Ímair.  Sitric was most probably among those Vikings expelled from Dublin in 902, whereafter he may have ruled territory in the eastern Danelaw in England.  In 917, he and his kinsman Ragnall ua Ímair sailed separate fleets to Ireland where they won several battles against local kings.  Sitric successfully recaptured Dublin and established himself as king, while Ragnall returned to England to become King of Northumbria.  In 919, Sitric won a victory at the Battle of Islandbridge over a coalition of local Irish kings who aimed to expel the Uí Ímair from Ireland.  Six Irish kings were killed in the battle, including Niall Glúndub, overking of the Northern Uí Néill and High King of Ireland.

Ottir: Earl Ottir (Old Norse: "Óttar jarl" ; Medieval Latin: "Oter comes" , 'Count Oter'; died 918), also known as Ottir the Black (Old Irish: "Ottir Dub" ), was a jarl who occupied a prominent position among the Norse of Britain and Ireland in the early 10th century.  He is believed to be the founder of the settlement, Loch dá Caech (present day Waterford) in the year 914.  From 917 to his death in 918 Ottir was a close associate of the powerful overking Ragnall ua Ímair, although they are not known to have been related.

Olaf Guthfrithson: Olaf Guthfrithson (Old Norse: "Óláfr Guðrøðsson" ; ; Old Irish: "Amlaíb mac Gofraid" ; died 941) was a 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.

Ragnall ua Ímair: Ragnall ua Ímair (Old Norse: "Rögnvaldr" , died 921) or Rægnald was a Viking leader who ruled Northumbria and the Isle of Man in the early 10th century.  He was a grandson of Ímar and a member of the Uí Ímair.  Ragnall was most probably among those Vikings expelled from Dublin in 902, whereafter he may have ruled territory in southern Scotland or the Isle of Man.  In 917, he and his kinsman Sitric Cáech sailed separate fleets to Ireland where they won several battles against local kings.  Sitric successfully recaptured Dublin and established himself as king, while Ragnall returned to England.  He fought against Constantín mac Áeda, King of Scotland, in the Battle of Corbridge in 918, and although the battle was not decisive it did allow Ragnall to establish himself as king at York.

Battle of Mag Femen: The Battle of Mag Femen took place on 22 August 917 between the Vikings of the Uí Ímair, led by Ragnall, a grandson of Ímar, and the Irish of the Northern Uí Néill, led by Niall Glúndub, High King of Ireland.  It was one of two battles involving the Uí Ímair that year, the other being the Battle of Confey, which occurred as a result of the Uí Ímair trying to retake the Kingdom of Dublin which they had lost in 902.  The battle began when Niall Glúndub's forces attacked a Viking army at a site identified by the annals as Topar Glethrach in Mag Femen.  The Irish initially inflicted the majority of the casualties, but late in the day a host of more troops led by Ragnall reinforced the Viking army, securing the victory for the Uí Ímair.

Ímar: Ímar (Old Norse: "Ívarr" ; died c. 873) was a Viking leader in Ireland and Scotland in the mid-late ninth century who founded the Uí Ímair dynasty, and whose descendants would go on to dominate the Irish Sea region for several centuries.  He was the son of the king of Lochlann, identified in the non-contemporary "Fragmentary Annals of Ireland" as Gofraid.  The "Fragmentary Annals" name Auisle and Amlaíb Conung as his brothers.  Another Viking leader, Halfdan Ragnarsson, is considered by some scholars to be another brother.  The Irish Annals title Amlaíb, Ímar and Auisle "kings of the foreigners".  Modern scholars use the title "kings of Dublin" after the Viking settlement which formed the base of their power.  Some scholars consider Ímar to be identical to Ivar the Boneless, a Viking commander of the Great Heathen Army named in contemporary English sources who also appears in the Icelandic sagas as a son of the legendary Viking Ragnar Lodbrok.

Ragnall Guthfrithson: Ragnall Guthfrithson (Old Norse: "Røgnvaldr Guðrøðsson" ; Old Irish: "Ragnall mac Gofraid" ) was a Viking leader who ruled 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.  He ruled Northumbria in 943 and 944, either with, or in opposition to, Olaf Cuaran.  Ragnall and Olaf were driven out of Northumbria by the English in 944.  His later life is unknown but it is possible he was the "king of the Danes" who is reported as being killed by the Saxons at York in 944 or 945.

Supporting paragraphs: Ragnall ua Ímair Ímar
Answer: 873