Tomrair mac Ailchi, or Thormod/Thorir Helgason, was the Viking jarl and prince who reestablished the preexisting small Norse base or settlement at Limerick as a powerful kingdom in 922 overnight when he is recorded arriving there with a huge fleet from an unknown place of departure. His ancestry is uncertain but he evidently did not belong to the Uí Ímair dynasty who only a few years before had reestablished themselves in the Kingdom of Dublin, of which Tomrair, the first King of Limerick, would immediately make himself the chief rival.
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References
Primary sources Annals of Clonmacnoise, translated by Connell MacGeoghagen (1627), ed. Denis Murphy (1896), The Annals of Clonmacnoise. Dublin: Royal Society of Antiquaries of Ireland. Annals of the Four Masters, ed. & tr. John O'Donovan (2nd ed., 1856), Annála Rioghachta Éireann. Annals of the Kingdom of Ireland by the Four Masters... with a Translation and Copious Notes. 7 vols. Dublin: Royal Irish Academy. CELT versions. Full scans at Internet Archive: Vol. I. Vol. II. Vol. III. Vol. IV. Vol. V. Vol. VI. Indices. Annals of Inisfallen, ed. & tr. Seán Mac Airt (1944), The Annals of Inisfallen (MS. Rawlinson B. 503). Dublin: DIAS. Electronic edition and translation at CELT. Annals of Ulster, ed. & tr. Seán Mac Airt and Gearóid Mac Niocaill (1983). The Annals of Ulster (to AD 1131). DIAS. edition and translation available at CELT. Chronicon Scotorum, ed. & tr. Gearóid Mac Niocaill (2003). Chronicon Scotorum. Unpublished manuscript made available to UCC. edition and translation available at CELT. Cogad Gáedel re Gallaib, ed. & tr. James Henthorn Todd (1867). Cogadh Gaedhel re Gallaibh: The War of the Gaedhil with the Gaill. London: Longmans. Secondary sources Downham, Clare, Viking Kings of Britain and Ireland: The Dynasty of Ívarr to A.D. 1014. Edinburgh: Dunedin. 2007. Lee, Timothy, "The Northmen of Limerick", in Journal of the Royal Historical and Archaeological Association of Ireland, Fourth Series, Vol. 9, No. 80 (Jul. – Oct., 1889): 227–231. JSTOR Ní Mhaonaigh, Máire, "Cogad Gáedel Re Gallaib and the Annals: A Comparison", in Ériu 47 (1996): 101–26. JSTOR Steenstrup, Johannes C. H. R., Normannerne, Vols. 3–4. Copenhagen: Forlagt af Rudolph Klein, I. Cohens Bogtrykkeri. 1882. alternative scan Valante, Mary A., The Vikings in Ireland: Settlement, Trade and Urbanization. Four Courts Press. 2008.