[cf. OIr. caill, wood, forest].
King at Tara who was twice humiliated, first by submitting to Fedlimid mac Crimthann in ad 838 and second when Fedlimid abducted Niall's queen Gormlaith (2) with all her female retinue. Earlier he was known for his decisive victory over the Airgialla in 827, slaying many of their leaders and making them dependent upon Tara.