"Balor of the Evil Eye" was king of the Formorians, a giant race of great antiquity that lasted at least to the time of Cúchulainn, oppressing newer inhabitants of the island. Balor had a large eye in the middle of his forehead that, when uncovered, caused burning destruction to whatever was before it.

Lugh Lamh Fada or Lug of the Long Arm, Balor's grandson, became king of the Tuatha De Danann and killed his grandfather in battle by slinging either a spear or a stone into the evil eye. Legend has it that when the dead giant fell to the earth, his still-burning eye dug an immense hole that became Lough Nasool (Loch na Súil), the Lake of the Eye, near Cong in County Mayo.

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