The Faceless Men are a group of assassins that pray to the Many Faced God, also known as the god of death. The Faceless Men can be found on Braavos and their home is the House of Black and White, the temple of the Many Faced God. The history of the Faceless Men is one rooted in much magic and mysticism. The first of the Faceless Men dates back thousands of years ago to the volcanic mines of Valyria, the same place where dragons were first discovered. An unknown man heard the many prayers of the different slaves working the mines, all praying to different gods. This man surmised that there must be one god, with many different faces, that these slaves were praying to.
The Faceless Men are deeply rooted in the religious ideals of the Many Faced God. At the House of Black and White, followers of the the Many Faced God perform religious services such as tending to the dead. They view death as inevitable, always stating Valar Morghulis, meaning “all men must die.” As such, they offer many services around death, such as a fountain of poison which offers a painless death for those who are ready to die. The most sacred service is that of planned death or assassination. For the right price, anybody can enlist the services of the guild of the House of Black and White to kill anybody in the world. It is the Faceless Men, the most elite of the House of Black and White, who are highly trained to carry out these assassinations.
In addition to their extreme training, it is understood that the Faceless Men also deal in some level as magic, as they are able to change the appearance of their faces. The most notable of the Faceless Men is Jaqen H’ghar, whose life was saved by Arya when she freed him from a burning cage that he was locked in, on their travel to the Wall. She also saved the two other men in that burning cart. Jaqen tells Arya that she stole three lives from the Many Faced God, and in exchange, he now owes her three deaths.