The world of Game of Thrones is filled with intrigue, murder, and secrecy. One group that embodies all those characteristics are the Faceless Men. These mysterious assassins operating out of Braavos but carry out their work all over the world. They specialize in quick and quiet kills that often look like accidents at first glance. And while it is costly to hire them, they claim to be able to kill anyone, no matter how powerful.

Through Arya Stark’s training and interaction with the Faceless Men, the show has revealed a lot about them. However, with George R.R. Martin’s book going into much greater detail, there’s still plenty that’s left out. Here are some facts about the Faceless Men that is not in Game of Thrones.

10. Their Origins

Arya at The House of Black and White Game of Thrones Season 5

Despite their low-key presence, the Faceless Men have been around for a long time. The order supposedly started in the slave mines of Valyria. An unknown figure heard slaves praying to various gods for death. The man gave a merciful kill to one slave and recruited another to join him. This process went on until the order grew.

With all the other storylines in the show, it’s no surprise the origin wasn’t covered. But it is interesting to know the group originated from slaves, and how they might be inclined to support a ruler with a history of emancipating slaves.

9. The Other Members

The Waif holding Arya's face on Game of Thrones

When Arya travels to Braavos, she visits the House of Black and White, the home of Faceless Men. But much like the X-Men mansion in the Deadpool movies, the house is pretty empty to due to budget restrictions.

The only members of the Faceless Men we meet are Jaqen H'ghar, the Waif and Jaqen H'ghar’s doppelganger. The book adds a few more members to the squad. Arya describes a kindly man who teaches her in the House of Black and White. There are also members she describes as the fat fellow, the handsome man, the squinter and the starved man, among others.

8. The Many-Faced God

Many-Faced God Game of Thrones

As Syrio Forel says, “There is only one god and his name is Death.” The Faceless Men do indeed pray and worship the God of Death, though they refer to this god as the Many-Faced God.

Westeros and other parts of this world wage wars in the name of what they believe to be the one true god. However, the Faceless Men believe everyone is, in fact, praying to the same god. They believe the God of Death is represented in each religion regardless of what he is called.

7. Women And Children Are Rarely Members

Arya Stark leaves the Faceless Men in Game of Thrones Season 6

While there do not seem to be set rules for who may join this order of assassins, they do take the title of Faceless Men literally. It is said that having women part of their group is very rare. Even rarer is having children trained as assassins.

The reason for these restrictions is unclear, but it is interesting to note considering how Arya Stark became involved with the Faceless Men. Despite being a female child, the group has taken a major exception with her. It seems she’s a natural born killer.

6. They Are Available To Anyone

Iron Coin Faceless Men Game of Thrones

To hire the Faceless Men to carry out an assassination is certainly costly. In the first novel, A Game of Thrones, Littlefinger shoots down the idea of using them to assassinate Daenerys Targaryen as the price is too high. But while it might always be a high price, the services of the Faceless Men are available to anyone willing to pay.

Even someone without a single coin can still hire the Faceless Men, so long as they are willing to give up something they value. The Faceless Men are not seeking to be rich, they just believe death has a price.

5. No Personal Kills

Arya Stark kills Walder Frey as revenge for the Red Wedding in Game of Thrones

Aside from the extensive set of skills one needs to become a member of the Faceless Men, there are also strict rules to obey. We saw in the show, that Arya was punished for killing someone whose name was not given, as well as refusing to kill someone whose name was given.

However, the most serious rule is that they cannot kill someone they know. A Faceless Man is meant to be a stranger and kills only to serve their god. Considering Arya has used her skills only for her own revenge kills, she may yet have to deal with the wrath of the Faceless Men.

4. How The Masks Work

One of the strangest aspects of the Faceless Men is the masks they use to change their identities at a moment’s notice. It’s a very handy trick, but the show hasn’t really shown how exactly it works. All we’ve seen is Arya’s creepy bag of faces that is pretty silly.

Thankfully, the books offer some more insight into things. Predictably, there’s some magic involved with the process. After drinking a special concoction, the Faceless Man cuts their own face and the blood allows the mask to fuse with their face. Still silly, but at least it’s a little more of an explanation.

3. The Memories Of The Mask

Faces in the House of Black and White in Game of Thrones

Another interesting aspect of the Faceless Men’s masks is the effect it has on those who wear them. The masks come from people who have given their lives to the Many-Faced God. When the Faceless Man puts on the mask, they inherit the memories of the deceased person.

While we have yet to see this happen on the show, it’s something really worth exploring in the final season. Surely exposure to all those other people’s memories would play with your mind. Arya has become a skilled killer, but it would be nice to see how that takes a toll.

2. They Likely Killed Balon Greyjoy

Balon Greyjoy looking serious while turning his back on his children in Game of Thrones

Despite the Faceless Men being prolific assassins, we have yet to see an actual member of their order kill a major character. In the books, they are equally low-key, but evidence suggests they were responsible for killing the Balon Greyjoy.

In the show, Balon is killed by his brother, Euron, who then freely admits to the deed. The books take a subtler approach. Balon is said to have fallen from a bridge in a storm and Euron soon returns from his exile in the East, where he would have had access to the Faceless Men. Though a small detail, it’s nice to see their skills used in a significant way.

1. The Citadel Conspiracy

Sam and Gilly at the Oldtown Citadel Game of Thrones Season 6 Finale

While the Faceless Men seem to operate only in the service of others and the Many-Faced God. However, in the later books in the series, there seems to be hints that they are involved in a larger conspiracy.

NEXT: Why George R.R. Martin Turned Down Game of Thrones Season 8 Cameo

In the prologue to A Feast For Crows, a novice working in the Citadel named Pate is killed after selling a key to a mysterious man whose description matches that of Jaqen H'ghar. The key in question can open any door in the Citadel. Later, when Sam travels to the Citadel, he meets a novice named Pate, suggesting the Faceless Men have infiltrated the Citadel. The question is, what are they up to?