The Night King (or alternatively Night’s King) is the leader of the White Walkers in the television series Game of Thrones. The character is possibly based on the legendary Night’s King who has only been mentioned in A Song of Ice and Fire. The Night King is the master and the first of the White Walkers, having existed since the age of the First Men. He also serves as the supreme leader of the Army of the Dead.
The Night King was a First Man that was captured by a pack of the Children of the Forest. Leaf, who was among the pack, pressed a dragonglass dagger into his chest, causing his eyes to turn blue and turning him into the first of the White Walkers. Thousands of years later, Leaf tells Bran Stark that her people created the White Walkers to defend themselves when Westeros was invaded by the First Men, who were cutting their sacred trees and slaughtering the Children of the Forest. However, the White Walkers soon turned on their creators and began what was known as the Long Night.
The Night King is a legendary figure, known by name among, at least, some noble houses in the North.