Throughout HBO's , only a select group of characters were actually able to kill White Walkers. The White Walkers are presented as a supernatural threat, coming from far beyond the Wall with the goal of creating an endless winter. They're a threat that no one in Westeros is equipped to handle as centuries have passed and stories of their existence have become legends. Dozens of characters managed to kill wights, the undead hordes who fight for the White Walkers, but the Walkers themselves can only be killed with dragonglass or Valyrian steel, making them highly powerful foes that were only killed a handful of times in the series.
Conflict with the White Walkers grew throughout the eight seasons of . Primarily explored through Jon Snow and Bran Stark's point of view, the Walkers remained beyond the Wall for seven seasons until finally advancing into the Seven Kingdoms for season 8. Characters in the North were left to prepare for their arrival, as the Walkers left behind mysterious symbols, collected babies to make new White Walkers, and launched attacks on Wildling encampments, giving the show's heroes a chance to face off with them on multiple occasions.
Jeor Mormont's great ranging takes several important characters beyond the Wall in hopes of finding Benjen Stark, discovering Mance Rayder's plan, and potentially discovering more information about the wights who attacked Mormont at Castle Black. The ranging is very costly for the Night's Watch, even claiming the life of Lord Commander Mormont and resulting in many characters being split up. Samwell Tarly ends up incidentally making an integral discovery after finding a dragonglass dagger at the Fist of the First Men, which he uses to kill a White Walker.
Sam is as shocked as anyone when the White Walker shatters at his hands, as he'd simply used the dragonglass out of instinct after the Walker had destroyed his sword. Sam's curious and scholarly mind figured that the dragonglass may have some significance, but he couldn't have predicted how essential a weapon it would be throughout the series. It takes time for members of the Night's Watch to believe what he's done, with Gilly being a less-than-reputable singular source in the eyes of Sam's brothers, but it's a moment of bravery that highlights the importance of his intellect and academic curiosity to the coming war.
Jon Snow manages to kill two White Walkers throughout , with the first instance having the most significance. In season 5, Jon Snow seeks to help the wildlings reach safety south of the Wall, and Hardhome still holds thousands of them. Jon and Tormund reason with them to migrate south before the encampment is attacked by wights. Jon, the Night's Watch, and the wildlings band together to defend themselves, but they're overrun by the seemingly endless wights led by a White Walker. This gives Jon his first opportunity to face off against one, which he manages to kill with his Valyrian steel sword.
Learning that Valyrian steel kills White Walkers doesn't give the people of Westeros much of an edge as the weapons are far and few between. But the knowledge at least gives Jon the confidence that he can face the Walkers himself if he needs to. In the trip beyond the Wall in season 7, Jon Snow and his team get the jump on a White Walker and party of wights, where Jon manages to claim his second kill with ease. As the White Walker shatters, the surrounding wights all perish, aside from the one that they'd bring back to King's Landing to show Cersei.
The season 7 battle importantly shows that the White Walkers work like necromancers and that they control surrounding wights. Killing one Walker means taking out a large chunk of the opposing force in one go. While many predicted that Jon Snow would be the one to kill the Night King, the season 7 White Walker would be the last that he killed, despite being one of .
Introduced in season 3, Meera Reed deserves to be mentioned among . Meera stays by Bran's side through everything and is the only human or direwolf that survives their trip beyond the Wall. In the season 6 episode, "The Door," Bran Stark discovers the origins of the White Walkers and how they were created by the Children of the Forest. He then uses his warg powers to scout the army of the dead before he realizes that the Night King can see him. The Night King grabs Bran's arm, allowing him to locate the Three-Eyed Raven's cave.
Shortly after, the White Walkers lead an assault on the caves in which the Three-Eyed Raven, Children of the Forest, Bran's direwolf Summer, and Hodor are killed. Amid the battle, Meera hurls a dragonglass-tipped spear at a White Walker, causing the being to shatter in front of her. Meera is surprised by the kill, but it isn't brought up again. Meera delivers Bran home to Winterfell in season 7, then returns to her home in Greywater Watch after Bran's lack of humanity upsets her.
The importance of the Night King and the Long Night was hyped up for years, and handling the situation in one episode was part of . In "The Long Night," Melisandre reminds Arya Stark of something she told her ages ago in season 3, that Arya would be responsible for ending the lives of many, shutting brown eyes, green eyes, and blue eyes. This moment suggests what Arya has to do, and she carries out her attack on the Night King.
Arya pounces on the Night King aiming for a backstab, but he quickly reacts and turns to catch her. She drops her blade from one hand to the other, stabbing the Night King and shattering him, resulting in his entire army falling with him. Her weapon is the same Valyrian steel blade that was sent to assassinate Bran Stark in season 1. The choice to have Arya kill the Night King was decided by the showrunners to subvert expectations, as Jon Snow seemed like too likely of a candidate.