When Balor of the Evil Eye and his wife Caitellin gave birth to their first child, a daughter named Eithlinn, it was prophesied that her child would kill Balor. Not wanting to kill his only child, instead, he determined to build her a tower made of glass and shut her inside it. Twelve bondswomen would care for her. She would never look upon a man or hear one's name spoken. She would live her life pampered, but away from people. Having no contact with any others, she would never bear the child who would cause Balor's death. Thus could the prophecy be averted. And so it was done as he commanded.
When Eithlinn had reached womanhood, Balor stole by guile a magical cow called the Glas Gaibhleann from a Tuatha de Danaan named Cian. Cian, seeking the help of a seeress named Birog, discovered the theft and, with Birog's advice, decided to steal Balor's most precious treasure in hopes of ransoming his cow. This story is better told elsewhere, but when Cian met Eithlinn, they fell in love instantly. They consummated their love before Cian, realizing that stealing her would cause war with the fomorians, left, though he promised to return to her.
Birth & Rescue
Eithlinn stayed with her guardians, and in due time give birth to triplets. The first was golden-haired like his sire, while the others were dark like their mother. Word was brought to Balor of their birth and he flew into a rage. Descending on the tower, he ripped the children from their mother's breast. Still, he could hardly bear the thought of slaying his own kin. Wrapping each in a blanket, he flung them into the sea, crying, "Let the sea decide the fate of my grandchildren! If they be drowned, then none shall survive to be my doom. If fate depress otherwise, let them be borne up upon waves and saved."
The waves rolled in and each child seems to be swept under the water. Unknown to Balor, however, Manannan Mac Lir, Tuathan overlord of the sea, saw all that transpired and heard Balor's speech. He took pity on the children. The golden-haired boy he swept in a wave to Cian and made known to him that this was his son. The second, a dark girl, he changed into a seal, giving her the power to shift her shape and become the first of the selkie. The last, a dark boy, he made into a fishtailed man, creating thereby the merfolk. So, by Balor's rash act, two faerie kith came into existence, and his doom was sealed.
Childhood & Kingship
Cian named the golden boy Lugh, which means "light." He loved his son, for the child reminded him of Eithlinn. Knowing he had no way to care for the infant, though, Cian asked that any Tuatha of good character who would provide a nursemaid step forward and claim fosterage of his son. A mysterious stranger wrapped about with mists answered his plea, bringing with him his with Fand to suckle the child. Cian gave Lugh into the stranger's keeping once the man had proven himself a mighty warrior and a clever poet. Thus, Manannan Mac Lir legally became Lugh's foster father and taught him all the arts of the Tuatha. The boy grew to manhood and Manannan advised him to seek a place at court.
So Lugh went to court and found welcome there, bringing with him many great treasures given him by his foster father. When all saw the talents Lugh displayed, they were amazed, for he knew all the great arts of the Tuatha: warcraft, smithing, healing, poetry, and many others too numerous to list. Nuada himself (having recently reclaimed his throne from Bres) gave the crown to Lugh saying that he was the best of them all and deserved to be king. They overlooked the fact that Lugh's arms were slightly too long for his body to be entirely proportional; a gift of his mother's fomorian blood.
Battle & the Death of Balor
Soon, the Tuatha heard that Balor was coming to avenge the deposition of Bres and bringing with him enough ships to bridge the gap between his own island and Hibernia and warriors to fill all those ships. Quickly, they assembled their own hosts and went to meet his armies. At the head of their hosts rode Lugh of the Long Arm, their new king. When they came into range, Balor opened his eye and the red light played across the hosts of the Tuatha and their lesser children, the sidhe. Everywhere that light fell, warriors writhed and fell dead, poisoned by the evil of Balor's eye... all except Lugh. He clutched to him a great spear that protected whomever held it from all harm. The red light played all about him, yet he did not fall. Kicking his horse into a gallop, he headed straight for Balor, whose eye had closed again. His grandfather never saw him coming.
With a great cry, Lugh rushed up to Balor, who stood alone before his own troops lest he slay them, and drove the spear into the eye just as it began to open once again. The great spear passed through the eye and into Balor's brain, killing him instantly. Given new heart, the Tuatha attacked and drove the fomorians from the land.
Though Lugh is House Balor's first direct ancestor, they regard him as a traitor to the house. Even today, they search for signs in those born of Balor that he has reincarnated. Whenever they find signs that point to that possibility, the child is taken and watched. Should he evince attitudes detrimental to the house, the child is killed. They will not submit themselves to the Tuatha ever again!