Olaf the White was king in Ireland from 853 to 871.
The Annals of Ulster name the Norse leader who was defeated by Óláfr and Ívarr in 857 as Caittil Find ... a name which, in keeping with the mixed cultural origins of the Gall-Gaedhil, is part Norse and part Gaelic. It is made up of Old Norse Ketill and Old Irish Find meaning 'fair'. The possiblity immediately suggests itself that this Ketill who was defeated by Óláfr and Ívarr in Ireland in 857 was no other than Ketill flatnefr [Ketil Flatnose], a prominent ninth century viking who is shown in the saga literature to have had close associations with the British Isles and with Óláfr of Dublin.
While the Cogadh Gaedhel claims that Caittil was slain in the Munster battle, the Annals of Ulster record only his defeat ... It is clear from Norse accounts that the lands round about the British Isles were known to Kettil from his youth when he harried there far and wide. He eventually left Norway to settle in the Hebrides. He undoubtedly ended his days in the British Isles, but Norse sources do not specify precisely where he died.
Ketill flatnefr's children are universally given in the sagas as two sons Bjorn austrni and Helgi bjólan and three daughters, Auðr, Þórunn and Jórunn. Eyrbyggja saga relates that Bjorn followed his family to the Hebrides ten years after Ingólfr Arnarson had settled in Iceland. This suggests a date c884 for Bjorn's voyage to the west. When he reached the Hebrides he found that his father Ketill had already died- a clear indication that Ketill flatnefr's lifespan centred on the middle of the ninth century.
Auðrinn djúpauðga appears to have married Olaf before he sailed for Dublin and before Ketill sailed for the Hebrides. Later, Auðr is always associated with her father, not with her husband, who put her aside in favour of an Irish princess. Several Scandinavian sources state that during his sojourn in the Hebrides Ketill had a serious quarrel with the Norwegian king, which arose from the refusal of Ketill to pay tribute as chieftain of the Hebrides. Þórunn hyrna, one of Ketill's daughters, was, according to Scandinavian accounts married to Helgi magri the Norse grandson of the Irish king, Cerball of Ossory. Cerball died in 888. One of Ketill's grandsons Þorsteinn raudðr married Þuríðr the granddaughter of this same Cerball ... helping to date Ketill's active career to c840-80.
Ketill was closely associated with a particular king of the mid-ninth century in an effort to bring the Norse colonies into closer alignment with the Norwegian homeland. His third daughter, Jórunn manvitsbrekka, had a son called Ketill inn fíflski [Little Wolf Kettle] who later settled in Iceland, and we find from Landnámabók that he came out to Iceland from the Hebrides ... Christians among Ketill's kin spent some time in the Hebrides. Later, when these Hebridean Norsemen settled in Iceland, they were conspicuous for their Christianity at the end of the ninth century, when almost all the settlers were still pagan ... this wholesale conversion of Ketill's family to the new beliefs must presuppose a prolonged stay in the semi-Gaelic environment of the Western Isles in which Norsemen at an early stage had come into contact with Christians organised under the church of Iona.
Source: Scandinavian kings of the British Isles 850-880 by Alfred P Smyth pub Oxford University Press
Source: "A biographical dictionary of Dark Age Britain" by Williams, Smyth and Kirby.
26 December 1998