What spirit is known as the Face Stealer?

The spirit known as the Face Stealer is Koh.

Koh is an ancient, centipede-like spirit introduced during “The Siege of the North.” Aang visits him in the Spirit World because Koh may know the identities of the Moon and Ocean spirits. Koh is dangerous because he steals the faces of victims who show emotion in his presence, especially fear or anger.

The encounter establishes Koh as more than a generic monster: he is calculating, theatrical, and deeply connected to the Avatar world’s spiritual history. Aang must remain expressionless while speaking with him, making the scene a test of composure as well as a search for information. Koh’s stolen faces form a disturbing collection around his body.

Koh is sometimes mixed up with La and Tui, the Ocean and Moon spirits encountered in the same storyline, or with Hei Bai, a forest spirit. Later expanded lore reveals that Koh is the estranged son of the Mother of Faces, a spirit capable of restoring or changing faces.