List of characters in the Camp Half-Blood series
Mrs. O'Leary - Mrs. O'Leary is the only friendly hellhound to ever exist. Quintus (Daedalus) was her original owner, but, after asking Nico Di Angelo to kill him, Percy becomes the hellhound's owner. While Percy is in the "mortal world", Charles Beckendorf takes care of her at Camp Half-Blood.She rescues Percy while in the Labyrinth.