Airbertach (d. 1016), son of Cos Dobráin, was at the time of his death airchinnech or superior of the monastery of Ros Ailithir (Ross Carbery, Co. Cork). The only other reference to him in historical sources, an entry in the Annals of Inisfallen, states that in the year 990 Ros Ailithir was attacked by vikings. The raiders carried off the son of Cos Dobráin, the fer léigind (lector or chief scholar), but he was subsequently ransomed on Scattery Island, Co. Clare, by Brian Bórama (qv).
As fer léigind of Ros Ailithir, Airbertach was the head of a monastic school whose reputation for learning is reflected in later medieval writings. Apart from the annalistic notices just mentioned, he is known to us only from a series of didactic poems, attributed to him with varying degrees of certainty: a lengthy geographical poem based on the writings of Isidore and Orosius, headed in both of the manuscripts where it occurs with an ascription to ‘the fer léigind Mac Coise’; a composite work written in 982, mainly concerned with the study of the psalter and containing an apparently interpolated verse which tells of Airbertach son of Cos translating material from Latin into Irish; and two poems dealing with the kings of Judah and with a victory of the Israelites over the Midianites, also generally assigned to Airbertach because they occur in conjunction with the first two poems in Bodleian MS Rawlinson B 502, the only manuscript that contains all four. While it seems possible that Airbertach did produce all of these compositions, it is also possible that one or more of them are the work of other members of his school.
Gearóid Mac Eoin has argued that Airbertach was also the author of one of the principal monuments of Middle Irish verse, the biblical epic ‘Saltair na Rann’ (also surviving in Rawlinson B 502, and dated to 988 on the basis of an apparently intrinsic chronological passage). He has proposed that the apparently unfinished state of the ‘Saltair’ may be due to Airbertach's work having been interrupted at the time of his capture by vikings. This theory, and some of the other attributions to Airbertach, were however challenged by James Carney (qv).