Ferdiad

Ferdiad (also Fer Diad, Ferdia, Fear Diadh), 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 opposite sides to his best friend and foster-brother Cúchulainn, with whom he had trained in arms under the renowned warrior woman Scáthach. He and Cúchulainn are equal in all martial feats, with two exceptions: the Gáe Bulg, a barbed spear which Scáthach has taught only Cúchulainn to use; and Ferdiad's horny skin, which no weapon can pierce.