Sea King

Sea Kings are mythical sea creatures in the anime and manga One Piece, which are much larger than normal sea creatures to the point of being ridiculous (even the smallest sea kings are easily more than 100x the size of a ship). They are found in great numbers along the Calm Belt around the Grand Line, although in rare occasions they can be found in other places throughout the world (those are generally quite small and are likely driven out by the other much larger sea kings).

Sea Kings make trade and travel difficult for anyone trying to cross the water where they are found. Cases have arisen where some islands in the Grand Line close to the edge of the Calm Belt have ended up getting almost completely cut off from the rest of the world. In Water 7 and its surrounding islands, this led to the eventual creatation of the Sea Train as a means to travel safely to and from each of its surrounding islands.

Sea Kings are serpent-like in appearance, however they vary from one Sea King to another in exact appearance and size. Only the strongest of ships or captains can take on a Sea King. Most other creatures in the ocean fear the Sea King, with the notable exeption of Bananawani. Confrontation with one by all but a few humans is unadvisable. Many characters, such as Franky, see the act of killing one a sign of strength and achievement.

Very few Sea Kings end up with names, only those who commonly inhabited the same waters receive names. The Sea King that ate Shanks' arm is known as The Lord of the Coast, and Long Land Long Ring Island had a Sea King called Master of the Waters.