Aegishjalmur is a magical symbol of protection used by Vikings. Originally from Iceland, it is also known as a terror or fear spell.
These types of symbols were commonly used by Viking warriors as a protective sign painted on the forehead before the battle, known as herkumbl ("war sign"). Drawn between the eyes, it was granted the ability to make the bearer invincible and frighten their enemies.
He appears in several Nordic sagas, where he is mentioned by various names as a countenance of terror or dominant character.