Who is the old seaman? How does he behave at the inn?

The old seaman calls himself "Captain" but is in fact a man by the name of Billy Bones. It's fair to say that he's quite a character. As soon as enters the Admiral Benbow he starts behaving in a wild, raucous manner: cussing, drinking, sponging, and generally making a complete nuisance of himself. The salty old sea dog is a habitual drunkard, knocking back endless tankards of rum. Dr. Livesey warns him about his drinking, but Billy Bones is not prepared to listen. He also likes a bit of song, whether or not anyone else wants to join in. He introduces us to the famous old pirate song "Dead Man's Chest," with its refrain of "Yo-ho-ho, and a bottle of rum."
Jim's father, however, is scared stiff of the man. This isn't all that surprising when one considers his violent, unstable demeanor. But for many others, there's something wonderfully mysterious about his larger-than-life character, and Jim Hawkins, for one, is utterly fascinated by him. He spins a good yarn, this Billy Bones, and his tales of adventure on the high seas stir the imagination of the young lad. He tells Jim that he was first mate on board the ship of Captain Flint, a notorious pirate. This sets the scene for what is about to happen. For after the old sea dog finally breathes his last after one tankard of rum too many, Jim and his mother find a key hanging round the old pirate's neck. It's a key to an old chest. There's not much gold inside the chest, but there is a map inside—a treasure map. Having made this startling discovery, Jim Hawkins is about to embark upon the adventure of a lifetime.