Jacob Avery is the name of a fictional character in the Larkill Manor storyline. He is a boy who snuck into Larkill Manor in order to gain greater insight into a recurring dream that he had been having about the place. The events surrounding him are chronicled in his journal which can be found in one of the rooms of the haunted house. His name appears to be a mixture of the title of the movie "Jacob's Ladder", and the name of the screenplau writer of the movie Silent Hill, Roger Avery.
When Jacob snuck into the abandoned Larkill Manor, he brought with him a journal. In it, he recorded his experiences in the house. His journal can still be found in one of the rooms of the haunted house, and reading it may give the customer greater insight into the happenings in the house including the nature of the hideous creatures found within it.