Ferdiad, son of Damán, son of Dáire, of the Fir Domnann, is a warrior of Connacht in the Ulster Cycle of Irish mythology. In the Táin Bó Cúailnge, Ferdiad finds himself on the side of the war opposite to that taken by his best friend and foster-brother Cú Chulainn, with whom he had trained in arms under the renowned warrior woman Scáthach. He and Cú Chulainn are equal in all martial feats, with two exceptions: the Gáe Bulg, a barbed spear which Scáthach has taught only Cú Chulainn to use; and Ferdiad's horn skin, which no weapon can pierce.