Much has been made of the threat posed by White Walkers, the undead villains of Game of Thrones. But what are they, where did they come from and what do they want? And why are some of them skeletons and others zombies?

We've got your answers. (See, we just saved you a weekend of binge-watching and Googling.)

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What are White Walkers?

The White Walkers are actually two groups: White Walkers proper and wights.

Their other name, the army of the dead, is a helpful way of understanding the distinction: The White Walkers are the officers and the wights are foot soldiers.

How can I tell White Walkers from wights?

White Walkers have the tell-tale ice-blue eyes and look like people with no skin, just muscle. Many look like aging hippies with long white hear and beards. And so far, they've all been men.

They are often on horses, carry ice spears and sometimes wear armor.

Wights tend to look like skeletons or zombies, with the latter often possessing the trademark blue eyes. They also behave like stereotypical zombies, either trudging slowly through the snow or descending on their victims in droves (for instance, Hodor).

Wights can be of any age or gender.

Any dead creature can be turned into a wight: We've seen wight horses, wight giants and as of the penultimate episode of Season 7, polar bears and dragons.

How are White Walkers made?

Male infants are turned into White Walkers. Remember Craster, the nasty wilding who let the Night's Watch crash at his place in exchange for not asking questions about where all his sons went? He left them in the woods as sacrifices to the White Walkers, who picked them up and took them to the Night King (more about him later), who converted the babies with the touch of his finger, turning their eyes ice-blue. But we don't know what happens to them between their infancy and adulthood. (Which makes us wonder, is there a Hogwart's for White Walkers?)

Wights can be turned at any age. We know the Night King can resurrect thousands of dead people at once just by raising his arms. It's not clear if the other White Walkers have this same power, but it appears the ones in armor might be capable of creating wights. Benjen Stark, uncle to the Stark children, said a White Walker tried to turn him by stabbing him with dragonglass.

Who's in charge here?

The Night King, who wears armor and an ice crown. Other White Walkers in armor appear to be his generals and have been seen leading packs of wights.

What's the deal with the Night King?

He was one of the First Men, the original group of human settlers in Westeros thousands of years ago. But the indigenous people (a magical group known as the Children of the Forest, who look like little Jolly Green Giants) saw them as a threat. So they kidnapped one and plunged a dagger made of dragonglass into his heart, creating the very first White Walker, a race intended to protect them from the First Men. But along the way, the White Walkers turned on both the Children of the Forest and the First Men. It's not clear why or when that happened.

How do you kill White Walkers?

We know what won't work: Regular steel swords won't kill either White Walkers or Wights.

Fire does work on wights, who are very flammable. But White Walkers seem to be able to walk through it unscathed.

Swords made of Valyrian steel (which are forged with dragon fire, according to legend) can kill them.

But given that dragons were extinct for thousands of years and the Valyrian Freehold is no more, there's a finite amount of Valyrian steel and people who know how to work with it. Now that there are dragons again and we know Gendry is a skilled blacksmith, that could change.

Dragonglass, a type of volcanic glass, also works on White Walkers. The First Men used it to defend themselves against White Walkers and Sam Tarly discovered its killing potential when he stabbed one with it after it shattered his sword.

It's also in far greater supply than Valyrian steel. Dragonstone, the Targaryen family castle, sits on a mountain of the stuff and Daenerys has given (secret nephew) Jon Snow the OK to take all he needs to arm humans.

What do the White Walkers want?

Permanent winter. But at the very least, they want to come south of the Wall and create more soldiers for army of the dead. But they can only do that in winter. (Keep in mind, seasons can last for centuries in the Game of Thrones universe.)

The last time this happened was during the Long Night, the worst winter in recorded history, thousands of years before the show started. The population of Westeros starved and froze to death in droves, making it a target-rich environment.

The Children of the Forest and the First Men came together to drive them back up north and then the First Men built the Wall, a 300-mile long, 700-foot high bulwark on the northern border of the Seven Kingdoms, engraved it with magic to block the dead from passing through) and staffed it with the Night's Watch (who also kept out the Wildlings and other perceived threats). As long as it stands, they can't come through (though that mark on Bran Stark's arm may change that equation).

What are the odds the Wall will still be standing by the end of the series? Place your bets.

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