Night King

The Night King was the master and first of the White Walkers, and the supreme leader and puppet-master of the Army of the Dead. Originally a First Man, the Night King was taken hostage by the Children of the Forest and turned into the first of the White Walkers. Despite originally creating them to combat the First Men, the Night King and the White Walkers soon turned on the Children of the Forest, leading to the Long Night and the War for the Dawn, where the Children and the First Men pushed the Walkers back to the Lands of Always Winter. The Night King and the Walkers remained hidden away far to the north for thousands of years and quickly faded into the myth and legend, until over ten thousand years later when the Night King led the Army of the Dead to break through the Wall and invade Westeros during the Great War. The Night King, the White Walkers, and the Army of the Dead were vanquished for good during the Battle of King's Landing at the hands of Bran Stark. Since the Night King created every other Walker and the White Walkers created the Army of the Dead, the death of the Night King led to the immediate and simultaneous death of every other White Walker and wight in the Army of the Dead.