Blathmac (d. 825), son of Flann, prior or acting abbot of Iona, was guardian of the relics of Colum Cille (qv) during the absence of the abbot, Diarmait, and was murdered by the vikings. According to Walafrid Strabo's ‘Vita Blaithmaic’ (‘Si tantam meruere suo pro carmine famam’), a panegyric in hexameter verse written some years after his death, his name means ‘beautiful son’; even from infancy he was considered to have been gifted with special graces. He is described as being ‘of royal stock’ (regali de stirpe), a warrior prince, and ‘a future king of his people’ who relinquished his patrimony to enter the religious life. He was probably one of the Northern Uí Néill who withdrew to a monastery without his parents' permission, and distinguished himself by his zeal for the monastic life.
Blathmac eventually went to Iona and was appointed prior in the absence of Abbot Diarmait, who was twentieth in succession to Colum Cille. As the monastery had twice been attacked by vikings, Diarmait had fled to Kells taking most of the community with him, leaving only a token presence. Blathmac foresaw another viking raid and warned the community that ‘a great storm was about to burst upon them’. Forewarned of the raid, he ordered the relics, ‘contained in a casket of precious metal’ (preciosa metalla . . . arca), to be hidden in a trench. When the vikings came, ‘threatening cruel perils to the blessed men’, they slaughtered those who had remained in the monastery. They tortured Blathmac in order to discover the whereabouts of the sacred relics, and then murdered him. Strabo's account was probably commissioned by one of the Irish peregrini in Germany, since it is hard to know how otherwise the fame of his martyrdom, in such detail, could have reached as far as Reichenau on the shores of Lake Constance; the matter was probably of topical interest during the involvement of the Frankish court in Danish affairs in the 820s.
The Annals of Ulster record Blathmac's death in 824 (825) thus: ‘The martyrdom [martre] of Blathmac, Flann's son, by the gentiles in Iona of Colum Cille’. His remains were buried in Iona; his feast-day is 24 July.