How Balor came to be defeated
Although Balor was so powerful, a druid predicted that he would die by the hand of his own grandson. At this time Balor had only one child, his daughter Ethnea. Deducing that she was the only one by which his destruction could be wrought he had her shut up in an impregnable tower, which he or his ancestors had already built on the summit of Tor-more, an almost inaccessible rock at the eastern extremity of Tory Island.
He placed her under the charge of twelve matrons whom he instructed never to let sight or knowledge of any man near her. Although she was thus imprisoned she grew into a lovely young woman, but often asked her female attendants questions about the manner in which she had received existence, and about the strange beings she saw in the distance passing up and down the sea in currachs. The matrons faithful to their master never explained anything to the young woman keeping her in ignorance.
Balor believing himself to be safe from the prediction of the druid, continued his campaign of piracy, raiding the nearby Tír Conaill ( Co. Donegal ) and capturing vessels and goods from unwary sailors.
At that time there were three brothers named Gavida, Mac Samhthiann and Mac Kineely living in the Northwest of Ireland near the shore opposite Tory Island in the area of Rath Finan. Gavida was a smith who had his forge in a place called Drumnatinne. Mac Kineely was the chieftain of that district comprising the areas of Rath Finan and Tullaghobegly and he owned a cow called "Glas Gaibhnenn" and she produced so much milk that she was coveted by all his neighbours. So many attempts had been made at stealing her that he found it necessary to watch the animal constantly.
Balor wanted this cow above anything else and set out to get her using all his powers of strength and stratagem. One day Mac Kineely went to his brother's forge to get some swords made leading the cow along by a rope.
When he arrived at the forge he entrusted the cow to his brother Mac Samhthainn who was also at Gavida's forge on business. Mac Kineely went inside to make sure Gavida made the swords according to his instructions. However while Mac Samhthainn waited outside Balor appeared to him in the form of a red-haired boy and told him that he had heard his two brothers Gavida and Mac Kineely saying that they would use all of Mac Samhthainn's steel in the making of Mac Kineely's swords while they intended to use only iron in his own.
So Mac Samhthainn rushes into the forge handing the cow to the boy to mind, but as soon as he was inside Balor transported the "Glas Gaibhnenn" to Tory Island with the speed of a lightning flash. The place where he landed with the cow is still known as Port na Glaise ( the harbour of the grey cow ).
When the brothers realised they had been tricked they ran out of the forge in time to see Balor in the middle of the Sound of Tory. After much angry outbursts and frustration and wandering about distracted for many hours, Mac Kineely decided to consult a druid who lived nearby.
The druid told Mac Kineely that he could never recover the cow so long as Balor was living for in order to keep her the Fomorian would never close his "evil eye" but would petrify any man that would try to get near the cow. Mac Kineely had a friend among the people of the Sidhe (the lordly ones - Tuatha de Danann) called Biroge of the Mountain.
Biroge had an idea on how to bring about the destruction of Balor. She dressed Mac Kineely in female attire then transported him to the top of Tór Mór on Tory Island. There knocking on the tower door she demanded admittance for a noble lady whom she had rescued from the hands of a tyrant.... Fearing to disoblige a Ban-Shee (woman of the sidhe) the attendant matrons allowed both into the tower. As soon as Ethnea laid eyes on the "noble lady" she perceived a face like those that had constantly appeared in her dreams. She fell in love with Mac Kineely at once. Biroge then put the twelve matrons into a deep sleep.
Mac Kineely stayed with Ethnea for a good long while in which he wooed and won her, until at last he was transported back to Drumnatinne by Biroge. When the matrons awoke at last they convinced Ethnea that the appearance of Biroge and Mac Kineely could only have been a dream, still they warned her never to mention the event to her father Balor.
Thus did things remain until Ethnea gave birth to three sons. Balor on hearing this was enraged and ordered the three infants to be cast into the whirlpool to be drowned. They were rolled up in a sheet which was fastened with a pin but as they were being carried across the land the pin fell out and one of the babies fell into the harbour,( which is now known as Port a Deilg - the harbour of the pin) the other two were recovered and sent to their deaths in the whirlpool.
However Biroge managed to rescue the child who had fallen into the harbour and transported him off to Mac Kineely his father who then fostered him out to his brother Gavida, who then trained the child in smith craft which ranked as high as the bardic profession in those times.
Thinking he had outwitted fate by drowning his daughter's three children, Balor learned from his druid that it was Mac Kineely who had fathered the children. He set out to gain his revenge. He crossed over to Ballyconnell with a band of his fierce associates and seized Mac Kineely, he laid the chieftain's head upon a white stone while his comrades held his arms and legs and with a single stroke of his heavy sword he decapitated him. Mac Kineely's blood flowed all over the stone and crimsoned it to its very centre, it is now known as Cloghaneely (anglicised from Cloch Cinnfaeladh -the stone of the bloody head) and is situated near the village of Cross Roads, in the north west of Kilmacrenan in Co. Donegal.
Balor thought that he was now completely safe and even compelled Gavida to make all his military weapons. As the years went on the son of Mac Kineely grew up to be a robust young man and becoming an excellent smith, Balor of the Evil Eye knowing nothing of his birth became greatly attached to him. Mac Kineely's son was aware that Balor had murdered his father and he knew the story of his birth and his escape from death at the hands of his grandfather. He often had fits of despondency when he would visit the blood-stained stone and return from it with sullen brow.
One day Balor came to the forge to have some spears made, it happened that as Gavida was away on business that all of that days work was to be executed by his foster son. While speaking Balor happened to start boasting about his conquest of Mac Kineely and how he came to die, but this boastful speech was to prove his undoing. The young smith watched for his opportunity and taking a glowing rod from the furnace he thrust it through the evil eye of Balor. The burning bar went right through to the other side of the tyrant's head. Therefore the druid's prophecy was fulfilled and Balor died at the hand of his grandson.
There are many variations of the stories about Balor, one has him being slain by his grandson called Lugaidh Lámhfada as he fought at Moytura in Sligo and his wife Kethleen fought bravely by his side. He is also said to have fallen by a stone cast at him by a machine called a tabhall a catapult type contraption.