Game Of Thrones Reveals The Origin Of The White Walkers

05/22/2016 10:44 pm EDT

SPOILERS for the Game of Thrones episode "The Door" follow.

Tonight's episode of Game of Thrones, titled the "The Door," revealed the answer to one of the biggest mysteries in all of Game of Thrones, the origin of the White Walkers.

In the world of Game of Thrones, the White Walkers are a threat that have mostly fallen into the realm of myth. Like the Children of the Forest and the giants, most citizens of the Seven Kingdoms believe that they died off or, more likely, never existed at all.

Of course, the Wildlings living north of the Wall have known that the threat is real for a while. Now, thanks largely to the efforts of Jon Snow, the Night's Watch and a few others are also aware of what's coming.

But up until tonight's episode, no one has actually known where the White Walkers originated from. Fans of Game of Thrones were given a hint when it was revealed that the White Walkers were taking Craster's children to make more White Walkers, but then where did the first White Walker come from?

Some fans have speculated that the White Walkers once ruled a larger kingdom that fell at some point in ancient times, and that they were responsible for leaving behind some of the stranger artifacts that were found by the Andals. It turns out that's not quite the case, but they were right about a previous civilization being involved somehow.

In a vision of the past, Bran saw a group of the Children of the Forest with a man tied to a stone at a weirwood tree. The children stab the man in the heart with what may be a piece of ice or glass, and the man became the first White Walker.

When Bran wakes up, he questions Leaf, wondering why the Children would create such beings. Leaf explains that it was because they were at war with humans, and they were losing badly.

This must have occurred during the war between the Children and the First Men. According to the establishing history Westeros, when the First Men first arrived via the Arm of Dorne, a brutal war broke out between them and the Children. The two sides eventually came to a standstill and made an agreement called the Pact. The Pact granted the open land to the First Men, and the forests to the Children. The two sides managed to co-exist pretty well from there on out, with the Children teaching the First Men to worship the Old Gods. Could it be the creation of the White Walkers is what caused the standstill and the Pact?

It was 4,000 years after the Pact that the White Walkers invaded, causing the Long Night. The White Walkers were defeated by an alliance of Men and the Children, led by the Last Hero (who may or may not be connected to Azor Ahai). That's a pretty long time between White Walker appearances, though there's a gap more than twice as long between the Long Night and the current invasion. Makes you wonder what the White Walkers get up to when they're not trying to overrun the world.

Game of Thrones airs Sundays at 9 p.m. ET.

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