In Game of Thrones, the White Walkers have morphed from a seldom-seen myth to the greatest enemy in Westeros. The Night King’s army of the dead has moved very, very slowly, marching south from Hardhome to breach the Wall with the help of an ice dragon at the end of season seven. Now, they’re on the verge of sacking Winterfell itself and ushering in the Long Night, a mythical winter that would wipe out most life in Westeros.

Jon Snow, Daenerys Targaryen, and the collected forces at Winterfell are on the verge of a great battle with the icy-eyed, sword-wielding undead — the biggest battle Game of Thrones has ever shown — and its outcome could determine who lands on the Iron Throne. (Assuming that Cersei Lannister doesn’t outlast them all, anyway.) With that in mind, here’s everything you need to know about the Night King, the White Walkers, and the wights.

What are White Walkers?

Long story short, they used to be humans and now they’re ice monsters. They don’t appear to speak to one another, but they do use some sort of nonverbal communication. In George R.R. Martin’s books, they’re a much more reputable-looking bunch with chameleon-like armor that perfectly reflects their surroundings. They’re pretty ragtag on the show, although some wear leather armor. They’re been marching south under the orders of the Night King (we’ll get to him later), and they’re willing to destroy anyone who gets in their way. They aren’t indiscriminate, though: The Walkers created some sort of truce with Craster the wildling, who gave them his baby boys in return for being left in peace.

Where are all those undead babies?

Unclear. They may age and grow up — either as wights or White Walkers, we can’t say for sure — or they may be in an elaborate undead nanny share.

What’s the history of White Walkers?

Someone is probably writing her Ph.D. thesis on this topic right now — that’s how much information we have on the White Walkers. Let’s just stick with the basics. We first met the Walkers in the opening scene of the series, when three Night’s Watch rangers discovered a bevy of dead wildlings in the woods beyond the Wall. Two of them were ripped to shreds by the Walkers, and the third fled south to desert the Watch. (Remember how Ned beheaded a guy in front of his children? That was the same guy.)

Though the Walkers weren’t seen for centuries, they have been a part of Westerosi lore for just as long. Old Nan describes them to Bran in chilling tales about the first Long Night that took place millennia ago, in which “kings froze in their castles” and “mothers smothered their babies to keep them from starving.” Unfortunately, few of Old Nan’s contemporaries believed that the stories have any basis in reality.

Based on what we’ve seen, the White Walkers are at least 8,000 years old: In season six, we learned that the Children of the Forest created the very first Walker as a weapon to combat the first men to arrive on Westeros. (They did so by plunging a piece of dragonglass into a man’s heart.) That Walker eventually turned on them, but we don’t know why. It eventually led to a massive war between the Walkers and the First Men, which ended with the defeat of the Walkers at the Battle for the Dawn. Afterward, the Wall was built by the founder of House Stark — a man named Brandon Stark, a.k.a. Bran the Builder — in order to keep the White Walkers from returning south. Around the same time, the Night’s Watch was formed to serve as guardians of the realm.

What are wights?

Think of the wights as the GOT version of zombies: They’re the undead hordes who fight for the White Walkers. We don’t know exactly how wights are controlled, but the ability to raise the dead is one of the Walkers’ greatest weapons, since every fallen soldier can join their war against the living.

What about all those animals? How did the White Walkers raise a dragon from the dead?

The animals are just another form of wight. Any dead animal can be brought into the servitude of the Night King, even a dragon. (RIP, Viserion.)

How do you make a White Walker?

That’s a tricky question! We know how the very first Walker was created, but we don’t know if that’s the only way. It’s assumed that the Children of the Forest made a small army of the Walkers to fight the First Men, but then they rebelled against them. These days, White Walkers can turn any dead body into a wight, but it’s worth noting they can also do something similar to living people, too. In season four, the Night King turned Craster’s son into something with icy blue eyes; whether the child became a wight or a Walker, it’s bad news for anyone who gets in his way.

How do you kill a White Walker?

Sam Tarly is the one who unwittingly discovered a way to kill White Walkers: dragonglass, which is basically the GOT version of obsidian. In season two, he found a cache of dragonglass at the Fist of the First Men while he hid from a swarm of Walkers, which suggests that Westeros’s ancestors used it as a weapon during the Long Night. In season three, Sam stabbed a White Walker in the shoulder with the dragonglass and the creature instantly shattered. More recently, through a combination of absurd good luck and dedicated library time, Sam learned that a literal mountain of dragonglass was hiding on, wait for it, Dragonstone. Jon Snow’s men dug it out and brought it to Winterfell, where Gendry has been forging it into weapons ahead of the big battle.

The second weapon known to destroy White Walkers is Valyrian steel. Unfortunately, there are only a few Valyrian steel weapons left in Westeros: Jon Snow’s Longclaw, Jaime Lannister’s Widow’s Wail, Brienne of Tarth’s Oathkeeper, Sam Tarly’s Heartsbane (which he gave to Jorah Mormont), and Arya’s Valyrian steel dagger.

It doesn’t seem like fire can kill a Walker — to say nothing of dragonfire, which burns much hotter — but it’s still a valuable weapon in any battle against them. As Jon discovered back in season one, fire is the easiest way to destroy a wight. (That’s why the Night’s Watch burned corpses.)

Who’s the White Walker that killed Viserion?

That’s the Night King. You can tell him apart from the other Walkers by his pointed crown. He appears to control the wight population through some sort of telepathy — or possibly something akin to Bran’s warging ability — and he can raise scores of the dead at once, as demonstrated at Hardhome in season five.

After Bran flashed back to the Children of the Forest creating the first White Walker, GOT seemed to confirm that the first Walker is also the Night King. However, Martin has suggested that the current Night King is not the same as the first one. (According to the books, the Night King of legend was an early commander of the Night’s Watch, though the show hasn’t followed that route.) There are a ton of theories about who the Night King is — including an absurdly popular one that says he’s a time-traveling Bran — but if we’re sticking to the show, it’s pretty clear that the Night King is the guy from Bran’s vision.

How do you kill the Night King?

Presumably, the Night King can be killed with dragonglass or Valyrian steel like any other White Walker. But let’s be honest: It’ll take a lot more than that. It wouldn’t be surprising if he possesses magical powers beyond what we’ve seen, plus he’s great at throwing those giant icy spears and he has a dragon of his own. If Jon or any other mortal comes face-to-face with him during the Battle of Winterfell, it’s hard to know if they could win.

But when Jon’s crew was trapped beyond the Wall last season, Beric Dondarrion made an intriguing observation: When a White Walker is killed, the wights he created immediately die as well. “Kill him,” Beric said, pointing toward the Night King. “He turned them all.” The group surmised that by killing the Night King, the entire army of the dead would die too. In other words, he’s like the flaw in the Death Star’s construction: It will be mighty tough, but if someone can take him out, the entire army will come crashing down.

Are the White Walkers evil?

It seems that way, right? All we’ve seen them do is kill. But their deal with Craster indicates some ability to form alliances. They may put those logic skills to use again in the future, perhaps with Cersei Lannister, the only ruler who hasn’t yet sworn war against them. A fascinating theory from Reddit user JoeMagician explains that the Walkers’ actions are much more targeted than they appear on the surface, but until we have more reasons to believe otherwise, that’s just a theory.

Everything to Know About the Night King and White Walkers