Cormac ua Cillín, Abbot of Tuamgraney, died 966.
Cormac was the ancestor of the Ó Cillín family, who were coarbs of Tuamgraney. The Chronicon Scotorum, sub anno 966, states:
Ua Cillín founded St. Cronan's Church, Tuamgraney.
References
Cormac ua Cillín Wikipedia(Text) CC BY-SA