Balor

Balor was a leader of the Fomorians, a malevolent race that threatened the Irish people. He is a one-eyed giant that wreaks destruction when opened.

According to legend, when Balor was a boy, he looked into a brewing potion and the fumes caused him to grow an enormous poisonous eye. The eye had to be opened by aides, and it killed anything it observed.  

Balor takes part in the Battle of Mag Tuired and kills the Tuatha de Danann king. However, during the same battle, four warriors forced open his eyelid by grabbing the handle attached to it. His own grandson and member of the Tuatha de Danann, Lugh, shot a sling-stone at his open eye. The force of the stone sent the eye through the back of his head, injuring the Fomorian army before the weight of his body crushed 27 Fomorian soldiers.