1 Princess of Lochlainn who suffers unrequited love for Cúchulainn. Hearing stories of the hero's prowess but without having seen him, Derbforgaill and a servant take the forms of swans to seek Cúchulainn. Not knowing their identity, the hero casts a stone at one swan, who, fallen to the ground, becomes Derbforgaill. He sucks the blood from her wound, saving her, but because he has tasted her blood, is forbidden carnal relations with her; Cúchulainn then gives Derbforgaill to his foster-brother (or foster-son) Lugaid Riab nDerg. The marriage is happy, but Derbforgaill dies an ugly death. Provoked into a contest to prove her sexual allure, by seeing which woman can send her urine furthest through a pillar of snow, Derbforgaill wins, only to bring down the wrath of the other courtly women, who jealously mutilate and kill her. Cúchulainn vengefully slaughters 150 women of the household, but Lugaid perishes of grief or shock.
2 One of the most famous adulteresses of medieval Irish history. Wife of Tigernán Ua Ruairc [O'Rourke], she departed with Diarmait mac Murchada [Dermot MacMurrough], perhaps willingly (1152), but returned home the next year. The resultant bitterness between the families led to the Anglo-Normans coming to Ireland, and thus the end of Irish freedom. In repentance, Derbforgaill founded the Nuns’ church at Clonmacnoise.