Oisín , a fictional character prominent in the Fianna cycle, appears as the son of Find (qv) son of Cumall and was thus included among the descendants of Baíscne (Clann Baíscni). As leader of the Fianna, his father Find is closely associated with Cormac (qv) son of Art, king of Tara. His mother is given as Blaí Dherg, who supposedly could take the form of a doe, or was magically transformed into one, hence the name Oisín (little deer). Tradition assigns him a sister (or half-sister) named Samaír, who was married to Cormac Cas, son of Ailill Ólom (qv). He was said to have taken a wife from among the Corcorthrí of Corann, and to have had a son, Oscar. It was claimed that he was absent from Ireland at the time of the fateful battle of Gabair, and so survived although the rest of the Fianna were massacred. After a long sojourn with his mother and her people in the otherworld, he returned to Ireland on a white horse, but circumstances obliged him (against the direst warnings) to set foot on his native soil. As a result, he was overtaken by extreme old age and died – but not before he encountered St Patrick (qv), with whom he engaged in a dialogue (composed in the twelfth or thirteenth century and known as ‘Acallam na Senórach’) and from whom he received Christian baptism.
M. C. Dobbs, ‘The Ban-Shenchus’, Rev. Celt., xlviii (1931), 214; Keating, Forus feasa, i, 271; O'Grady, Silva Gadelica, i, 253–6; O'Brien, Corpus geneal. Hib., 22, 45; Ó hÓgáin, Myth, 150–52; H. Roe, ‘Acallamh na senórach: the confluence of lay and clerical oral traditions’, C. Byrne, M. Harry and P. Ó Siadhail (ed.), Celtic languages and Celtic peoples: Proceedings of the second North American Congress of Celtic Studies (Halifax N.S., 1992), 331–46; A. Dooley and H. Roe (trans. and ed.), Tales of the elders of Ireland (Acallam na senórach) (1999)