The arrival of the so-called "Dark Foreigners" in Ireland is first recorded in Irish annals in 849 when the Fragmentary Annals of Ireland state euphemistically that "Amlaib [Olaf] Conung, son of the king of Norway, came to Ireland…with a proclamation of many tributes and taxes from his father, and he departed suddenly". Clare Downham discusses the various theories of the meaning of the terms "Dark Foreigners" and "Fair Foreigners" used in early primary sources to describe the Viking raiders. The identity of the "king of Norway" in question is uncertain. A later passage in the Fragmentary Annals of Ireland names him "Gofraid/Gothfraid, son of Ragnall, son of Gothfraid Conung, son of Gofraid", and the same source records the death in 873 of "the Norwegian king, i.e. Gothfraid…of a sudden hideous disease". "Gofraid/Gothfraid" cannot be linked to any of the main contemporary Norwegian rulers who are shown in the document NORWAY KINGS, although it should be borne in mind that the government of Norway was fragmented at the time with numerous local rulers in different parts of the country who probably all referred to themselves as kings.
Whatever their precise origin, the Viking raiders in Ireland quickly settled around Dublin, following the more permanent arrival of Olaf and his presumed brothers Ivar and Asl which is recorded in both the Chronicon Scottorum and the Annals of Ulster in 853. The Irish resources record numerous raids by these Dublin-based Vikings against their Irish neighbours. However, more surprisingly, they also record Viking alliances with different Irish factions to conduct joint attacks. For example, the Annals of the Four Masters record in 860 that “Aedh Finnlaith son of Niall Caille and Flann son of Conang went with the lord of the foreigners to plunder Meath”. More specifically, the Annals of Ulster record in 863 that "three kings of the foreigners, Amlaib and Imar and Auisle plundered the land of Flann, son of Conaing, and Lorcan son of Cathal king of Mide was with them in this". It is clear from these two contrasting passages that Irish/Viking alliances fluctuated and no doubt were motivated by short-term interest.
Ivar and his descendants are recorded in the Irish annals as kings of Dublin until the end of the 11th century. However, their leadership of the Viking settlers did not go unchallenged. The Annals of Ulster record in 893 "a great dissension among the foreigners of Ath Cliath and they became dispersed, one section following Imar´s son, and the other Sigfrith the jarl”. The same source records the return to Ireland in 894 of "Imar´s son”, who is presumably identified with "Sitriuc son of Imar killed by other Norsemen” in 896. The reconstruction of events in succeeding years is unclear from the Irish sources, until the Annals of Ulster record in 903 that "the heathens were driven from Ireland i.e. from the fortress of Ath Cliath by Mael Finnia son of Flannacan with the men of Brega and by Cerball son of Muirican with the Laigin”. Welsh primary sources record the arrival of Vikings in North Wales around the same time, presumably the consequence of their expulsion from Dublin. The Annales Cambriæ record in 903 that "Igmunt" [Ingmund] arrived "in insula Mon" (presumably referring to Anglesey) and held "maes Osmeliaun". The Chronicle of the Princes of Wales dates the event to 900, recording that "Igmond came to the isle of Mona and fought the battle of Rhos Meilon". The same Viking group passed on to England, as confirmed by the Fragmentary Annals of Ireland which record in  that "the Norwegians left Ireland…their leader was Ingimund", that they were "driven by force out of British territory" by "Cadell son of Rhodri…king of the Britons" [indicating that the passage refers to the Welsh], and that "Aethelflaed Queen of the Saxons [wife of Aethelred]…gave him land near Chester, and he stayed there for a time". Ingmund has not yet been identified: he does not feature in the Irish annals. Other Viking exiles from Dublin raided Scotland, as shown by the Annals of Ulster which record the death in 904 of "Imar grandson of Imar” killed by “the men of Foirtriu” [indicating Scotland near the Forth]. The regrouping of Viking forces can be dated to [914/16]. The Anglo-Saxon Chronicle records in 915 (manuscript D) or 917 (manuscript A) that "a great pirate host came over hither from the south from Brittany under two jarls Ohtor and Hroald, and sailed west about until the estuary of the Severn", and were opposed "by the men from Hereford and Gloucester…[who] slew the jarl Hroald and the other jarl Ohtor´s brother. The Annals of Ulster record in 914 "a naval battle at Manu between Barid son of Oitir and Ragnall grandson of Imar, in which Barid and almost all his army were destroyed”, and “a great new fleet of the heathens on Loch da Caech”, followed in 915 by "a great and frequent increase in the number of heathens arriving at Loch da Chaech". The family of Ivar was able to leverage the situation to its advantage, the Annals of Ulster recording that "Sitriuc grandson of Imar landed with his fleet at Cenn Fuait on the coast of Laigin” and “Ragnall grandson of Imar with his second fleet moved against the foreigners of Loch dá Chaech” in 917.
After that time, the descendants of Ivar established themselves once more in Dublin: the Annals of the Four Masters record that “Godfrey grandson of Imhar took up his residence at Ath-Cliath” in 919. After that time, Viking settlers were not confined to Dublin. Downham lists 19 places throughout Ireland, ranging from Ulster in the north to Galway in the west, Limerick in the south-west and Waterford and Wexford in the south-east, in which 10th century chronicles record Viking settlements during the period 917 to 968. The same family group diversified their field of activity into northern England: Simeon of Durham records that "King Inguald stormed York" in 919. Family members continued to rule as kings of York until they were finally driven out in 952.