Dagán (d. 641), founder and first abbot of Inber Doíle (Ennereilly, Co. Wicklow) and a saint in the Irish tradition, was a member of the familia of Glendalough. According to the genealogies his father was Colmad, whose ancestry is traced to the Leinster dynasty of Dál Messin Corb. His mother is named as Cóeltigern or Cóemóc, supposedly a sister of Cóemgen (qv) of Glendalough; he is accorded three brothers including Libber (qv) (Mo-Libbo), Mo-Bóe, and Ménóc of Glenealy. Irish hagiographical tradition represents Dagán as a student of Mochóemóc (qv) at Liath Mór (Leigh (Leighmore), Co. Tipperary); the latter's Life (§§26–7) includes an episode in which the young Dagán is beheaded by raiders from Osraige, but is restored to life by his master and Cainnech (qv) of Achad Bó. A medieval Life of Petroc of Padstow by John of Tynemouth claims that Dagán completed his education under the British saint in Cornwall.
The Irish martyrologies at 13 September style Dagán of Inber Doíle presbyter (priest); notice of a bishop Dagán, in the tract ‘De episcopis’ and in the martyrologies at 12 March (the eve of the feast-day of Mo-Chóemóc), however, is accepted by John Colgan (qv) as referring to the same individual. If the identification is correct, Dagán may be the bishop who, at the height of the Paschal controversy (c.610), travelled to Rome to visit Pope Gregory the Great. The bishop stayed at Canterbury and, according to Bede (‘Historia ecclesiastica’, ii, §4), offended Archbishop Laurence by refusing to take his meal in the same building as the English prelate. Dagán son of Colmad founded a church at Inber Doíle, on the boundary of Dál Messin Corb and Uí Fhiachrach; he may also be associated with the church of Achad Dagáin, unlocated but possibly identical with Inber Doíle (HDGP, ‘Achad Dagáin’).
Dagán died in 641, the martyrology notice at 13 September perhaps recording the date of his death. The inclusion of Dagán in the Irish Litany among the familia of Cóemgen suggests that his foundation came under the authority of Glendalough; diocesan charters list Inber Doíle among the possessions confirmed to the abbot of Glendalough in 1172–6.