Who is black dog in the book Treasure Island?

In "Treasure Island" by Robert Louis Stevenson, Black Dog is a menacing character who confronts the protagonist, Jim Hawkins, at the Admiral Benbow Inn. He is a pirate and a former associate of Long John Silver, and his appearance signifies the dangers and dark elements of piracy. Black Dog's aggressive demeanor and violent tendencies create tension and foreshadow the treacherous adventures that lie ahead for Jim and his companions.