The Face of Horror is a major antagonist in Rick Riordan's 2010 novel The Red Pyramid, and a minor villain in The Serpent's Shadow. This demon who serves as Set's lieutenant.
The Red Pyramid
After Set rises, Face of Horror gathers the demons of Chaos in Phoenix, Arizona. When Set comes, Face of Horror gives Set the idea to build the Red Pyramid. As the story goes, Face of Horror continues to act as Set's advisor.
During the final battle, it is revealed that Face of Horror was possessed by Apophis. Apophis had wanted Set to build the Red Pyramid so it would generate a huge amount of Chaos energy that would free Apophis from his prison. Face of Horror is killed by Carter.
The Serpent's Shadow
Face of Horror takes part in the attack on Thoth's pyramid. When Carter and Walt come to help, Face of Horror strangles Carter while having Apophis speak through him. Apophis shows Carter the terrible things he is planning, but is cut off when Thoth kills Face of Horror.