Question: In which year, was the son Gofraid ua Ímair who had succeeded his father recently as king defeated by the English led by Æthelstan?

Context paragraphs:
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.

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.

Battle of Brunanburh: The Battle of Brunanburh was fought in 937 between Æthelstan, King of England, and an alliance of Olaf Guthfrithson, King of Dublin; Constantine, King of Alba and Owen, King of Strathclyde.  One of the historiographical cruxes of this battle is the fact that it is often attributed to as the point of origin for English nationalism.  Additionally, historians such as Michael Livingston argue that "the men who fought and died on that field forged a political map of the future that remains [in modernity], arguably making the Battle of Brunanburh one of the most significant battles in the long history not just of England, but of the whole of the British Isles."

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.

Gofraid mac Sitriuc: Gofraid mac Sitriuc (died 951), in Old Norse Guðrøðr Sigtryggsson, was King of Dublin.  He was the son of Sihtric ua Ímair and a great-grandson of Ímar, founder of the Uí Ímair kindred which dominated much of the Norse-Gael and Scandinavianised parts of Britain and Ireland in the 10th century.

Lagmann mac Gofraid: Lagmann mac Gofraid may have been an early eleventh-century ruler of the Kingdom of the Isles.  He seems to have been a son of Gofraid mac Arailt, King of the Isles, and was likely a member of the Uí Ímair kindred.  According to an eleventh-century source, Lagmann was closely associated with Óláfr Haraldsson, a future King of Norway.  According to an eleventh-century source, both men are recorded to have lent assistance to Knútr, son of Sveinn Haraldsson, King of Denmark, although it is possible that this account actually refers to Óláfr's campaigning in England several years beforehand.  Lagmann and Óláfr are also recorded to have assisted Richard II, Duke of Normandy.  The two are specified to have not only ravaged lands in Brittany on behalf of Richard, but were tasked to counter Richard's opponent Odo II, Count of Chartres.  Lagmann's activities on the Continent may have arisen as a result of being forced from the Isles following the death of his possible brother Ragnall mac Gofraid, King of the Isles in 1004 or 1005.  Lagmann's son, Amlaíb, is recorded to have perished at the Battle of Clontarf in 1014.  If Lagmann died at about this time as well, it could account for the record of Hákon Eiríksson assuming control of the Isles.

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.

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 mac Gofraid: Ragnall mac Gofraid (died 1004/1005) was King of the Isles and likely a member of the Uí Ímair kindred.  He was a son of Gofraid mac Arailt, King of the Isles.  Ragnall and Gofraid flourished at a time when the Kingdom of the Isles seems to have suffered from Orcadian encroachment at the hands of Sigurðr Hlǫðvisson, Earl of Orkney.  Gofraid died in 989.  Although Ragnall is accorded the kingship upon his own death in 1004 or 1005, the succession after his father's death is uncertain.

Gofraid mac Amlaíb meic Ragnaill: Gofraid mac Amlaíb meic Ragnaill (died 1075) was a late eleventh-century King of Dublin.  Although the precise identities of his father and grandfather are uncertain, Gofraid was probably a kinsman of his royal predecessor, Echmarcach mac Ragnaill, King of Dublin and the Isles.  Gofraid lived in an era when control of the Kingdom of Dublin was fought over by competing Irish overlords.  In 1052, for example, Echmarcach was forced from the kingdom by the Uí Chennselaig King of Leinster, Diarmait mac Maíl na mBó.  When the latter died in 1072, Dublin was seized by the Uí Briain King of Munster, Toirdelbach Ua Briain, a man who either handed the Dublin kingship over to Gofraid, or at least consented to Gofraid's local rule.

Supporting paragraphs: Olaf Guthfrithson Battle of Brunanburh
Answer: 937