In Irish mythology, Balor (Balar, Bolar) of the Evil Eye was a king of the Fomorians. His father was Buarainech. His wife was Cethlenn. He is supposed to have lived on Tory Island.

One of Balor's eyes could kill anyone it looked upon; he gained this power as a child when he looked out the window when his father's druids were preparing poisonous spells, and the fumes rose into his eye. This eye was normally kept closed, and only opened on the battlefield by four men using a handle fitted to his eyelid.

According to a prophecy, Balor was to be killed by his grandson. He locked his daughter, Ethlinn, in a tower made of crystal to keep her from becoming pregnant. However, Cian, one of the Tuatha Dé Danann, with the help of the druidess Birog, managed to enter the tower. She gave birth to triplets by him, but Balor threw them into the ocean. Birog saved one, Lugh, and gave him to Manannan mac Lir, who became his foster father. He was called Lugh Lamhfada and became a member of the Tuatha Dé Danann.

Lugh led the Tuatha in the second Battle of Magh Tuiredh against the Fomorians. Ogma disarmed Balor during this battle, but Balor killed Nuada with his eye. Lugh shot a sling-stone which drove Balor's eye out the back of his head, where it continued to wreak its deadly power on the Fomorian army. In other versions Lugh blinded Balor with a spear made by Goibniu, or decapitated him and used his eye against the Fomorians.

In the fantasy role playing game of Dungeons & Dragons, the name Balor is used as the name of one the most powerful demons. Balor is the most powerful Tanar'ri (Chaotic Evil demons) type.

The name Fomorian is used in the game as the name of one of the Giant Kin Races. As far as the game goes, Balor and the Fomorians have no connection.