[Ir., the slender of Breg].
A leading figure in that portion of Irish legendary literature known as the Cycle of Kings. Cobthach seized power to become king of Tara by killing his brother Lóegaire Lorc, his brother's son Ailill Áine, and sending Ailill Áine's son Labraid Loingsech into exile. Many stories portray Cobthach as treating Labraid with wanton cruelty, such as forcing him to eat a mouse and its young, causing the boy to lose the power of speech. Labraid returned from exile in Gaul and burned Cobthach alive in ‘an iron house’ along with thirty allies. Cobthach may have been one of the early Uí Néill.