who is billy?

Billy is the main character and protagonist in the story, "The Landlady". He is 17 years old, and simply looking for a cheap place to spend the night. He wanders into a boarding house owned by an old woman, and the price is less than half what he expected to pay. He agrees to spend the night there, and the woman (The Landlady) is very kind to him. However, when he signs the guestbook, his calm personality shows a bit of worry - he has seen those names before. Weaver tries to protect himself from the realm of this strange house, and we ultimately don't know what happened to him. However, it is implied that he fails in the responsibility.