In George R.R. Martin’s A Song of Ice and Fire series, the Faceless Men are explored in far greater depth than in Game of Thrones. While the show primarily focuses on their connection to Arya Stark, the books provide much more insight into their philosophy, history, and internal structure.
First and foremost, the Faceless Men are not just killers but a cult devoted to the Many-Faced God. Their faith is based on the idea that death is a gift, an act of mercy that can be granted. The books describe their rituals in more detail, such as drinking from the Well of the House of Black and White to 'offer their faces' and become no one.
Arya’s training is also depicted with far more depth in the books. Her journey to becoming 'no one' is more detailed — she not only learns to change faces but also masters the arts of deception, observation, and patience. For example, she spends days blind, cleaning the temple, and fighting other trainees to sharpen her senses.

The books also hint more at the origins of the Faceless Men. One theory suggests that they emerged in Valyria, where slaves prayed for death to escape their suffering. The first Faceless Man may have been a slave who granted the 'gift' of death to his oppressors.
While in the show, the Faceless Men seem more like a plot device for Arya’s story, the books present them as a complex organization with a deep philosophy and history, adding even more mystery to the world of Westeros.
The Faceless Men are not just assassins but philosophers of death. They remind us that death is the only true constant in a world ruled by betrayal and intrigue. Their motto, 'Valar Morghulis' — 'All men must die' or 'All men are mortal' — is a chilling reminder of fate. And the Faceless Men are always ready to reinforce that truth.