Balor

"Balor of the Evil Eye" was king of the Formorians, a giant race of great antiquity that lasted at least to the time of CĂșchulainn, 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.

John Hunt 2015

Balor, by an unknown artist. Source: www.arrowrocklodge.com.