Besides being infamous for the Purple Wedding that marked the assassination of King Joffrey Baratheon at his wedding feast, Game of Thrones season 4, episode 2 "The Lion and the Rose," is home to Bran Stark's series of visions. He communes with a Weirwood tree and experiences several images from HBO's Game of Thrones' past, present as well as future events. Among swarming crows, the Three-Eyed Raven, the shadow of a dragon flying over the city of King's Landing, Ned's imprisonment, and so forth, the first of the White Walkers, i.e., Night King is also shown. That's as far as Game of Thrones' "The Lion and the Rose" goes about the Night King and humanoid monsters known as the White Walkers.

In Game of Thrones season 4, episode 4, "Oathkeeper," the Night’s Watch mutineer, Rast places Craster the dead Wildling's last baby boy in the woods and walks away. A White Walker collects the infant and takes him to the Lands of Always Winter. The Walker places the infant on an ice altar, and the Night King lays his fingernail on him and turns his eyes blue. While it's a couple more seasons until the Breaching of the Wall, it's clear that these ice zombies have sinister motives. As King Viserys I Targaryen puts it in the Game of Thrones prequel - House of the Dragon, this "absolute darkness" is intent on destroying the living. Viserys I relays Aegon's prophecy to his decreed heir, Princess Rhaenyra Targaryen:

'Tis s to begin with a terrible winter gusting out of the distant North. Aegon saw absolute darkness riding on those winds and whatever dwells within will destroy the world of the living … if the world of men is to survive, a Targaryen must be seated on the Iron Throne.

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Who Made The White Walkers

Long before the Battle of Winterfell, Game of Thrones season 5, episode 8, "Hardhome," boasts the bone-chilling appearance of the Night King and his lieutenants, i.e., the White Walkers. Their followers, the ice zombie army known as the Wights rampage through the Free Folk settlement - Hardhome. Known as the Massacre at Hardhome, the event sees the Night King, the White Walkers, and the Wights attack at a time when Jon Snow and the men of the Night's Watch are evacuating the Free Folk from Hardhome. The Wildlings are brutally massacred by the Wights and in the end, the Night King lifts his hands and raises tens of thousands of dead Free Folk as members of his army. That said, Jon kills a White Walker using his Valyrian steel sword - Longclaw and lets the evacuees pass the Wall. Apart from saving lives, Jon and Samwell Tarly learn that Valyrian steel can kill the White Walkers.

Game of Thrones Season 6, Episode 5 "The Door" delves into the origins of the White Walkers. Bran wargs back in time and finds Leaf and other Children of the Forest huddled together right in front of a Weirwood tree and a man tied to it. Bran watches in horror as Leaf plunges a shard of dragonglass into this man's heart. The man screams in agony, and when Leaf is done inserting the dragonglass, his eyes turn ice blue. "It was you. You made the White Walkers," says Bran after he's pulled back to the cave. Leaf replies saying, "We were at war. We were being slaughtered. Our sacred trees cut down. We needed to defend ourselves." When Bran asks who the Children of the Forest needed to defend themselves from, Leaf says, "From you. From men," and leaves him to it.

Bran revisits the once lush green locale in Game of Thrones' "The Door," only to see a frozen wasteland and the Army of the Dead in tens of thousands. He walks past the motionless Wights and comes across the Night King and the White Walkers sitting astride their dead horses. The Night King and Bran lock eyes and the latter turns around to see the Wights facing him. In the next scene, the Night King grabs Bran's right forearm, forcing him to scream, and end his vision. The Three-Eyed Raven asks Bran to leave the cave as the Night King knows him and is coming for him.

The First Men Invaded Westeros

As laid down in Game of Thrones' "The Door," the Children of the Forest created the White Walkers to use them in their war against the First Men. They were among the First Men themselves and were forcibly transformed to fight the invasion. This has inverse consequences as the White Walkers eventually rebelled, broke free, and turned into ruthless monsters. During the Age of Heroes, about eight thousand years before Aegon's Conquest, the living side fought and defeated the White Walkers. A winter, known in Game of Thrones lore as the Long Night, descended upon the world. It lasted a whole generation and in the midst of this, the Walkers invaded Westeros from the far North, culminating in the Battle for the Dawn.

The Walkers were pushed back to the Lands of Always Winter. The Wall was built with the help of giants, and the Children of the Forest to keep them out and the Night's Watch was formed to guard the realms of men against their threat. Many from the Night's Watch and the Free Folk sighted the Walkers in Game of Thrones. The first person to talk about them was a ranger named, Will who was executed by Ned Stark in Game of Thrones season 1, episode 1 "Winter Is Coming." Ned declared him "a madman" and refused to believe him. Those in the South of Westeros considered talk of the Walkers stuff of legend, and Jon and his men kept repeating that the Night King and the Army of the Dead were real. The Dead not only were a threat to the living but their leader, the Night King aimed to erase the world. The Night King and his army were defeated in the Battle of Winterfell by the alliance of the living. Arya Stark plunged a Valyrian steel dagger into the Night King's chest and he, his lieutenants shattered into tiny shards of ice one by one. The undead Viserion and the mindless Wights too dropped dead and the living side won the Great War.

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