|“|| 'Stand,' I ordered.
And as obedient as a shadow, it did.
The Rogue Hollow is the Hollowgast Jacob first controls and turns into a slave at the end of Hollow City. The hollowgast is presumably still alive at the end of Library of Souls as it has to power the Panloopticon.
The hollowgast is discovered frozen in place by Jacob in the Ymbyrne Council hall. Jacob doesn't tell anyone and ponders on if he should kill it or not. He then decides not to. Later, Jacob is lured back to it in his sleep and wakes up with his hand on the hollowgast's head. It is hinted that the hollow sent nightmares into Jacob's mind while he slept. Later, after Althea is stabbed by Caul, the hollowgast defrosts and chases after Jacob, into the modern world, where Jacob speaks to it in Hollow Tongue and bends its will to serve him.
Library of SoulsEdit
Jacob cannot seem to control it very well but the hollowgast remains obedient and follows Jacob everywhere he goes. When two wights catch up to Emma, Jacob, Addison, and Sergei, Jacob commands the hollowgast to kill the wight who was about to shoot Emma. The hollowgast obeys and brutally kills the wight by swinging him against the wall by the leg. Jacob tries to ditch the hollowgast, but then, while he escapes on the train, the hollowgast latches on with his tongues and follows Jacob. It was assumed to be dead when it crashed into a bridge in Devil's Acre. Jacob controlled many other hollowgasts after that. Soon later the hollow is found by pirates, and led back to a place used to train wrestlers. The hollowgast soon pretended to be defeated by Jacob on his orders and was later brought back and healed by Mother Dust. The hollowgast was then used as the heart of Bentham's Panloopticon. According to the book, the creature was screeching before the anesthesia was put in, which proves it might have been painful, as its blood was used to run the machine.
- The hollow possibly digested a peculiar soul, which could explain why it was in the loop it was frozen in.
- It was painted, and this enabled people to see it.