Is it a case of mistaken identity, or a nickname based on demeanor or skills or other attributes? (I haven't read much Tolkien, and not in decades.) Tarzan is

Is it a case of mistaken identity, or a nickname based on demeanor or skills or other attributes? (I haven't read much Tolkien, and not in decades.) Tarzan is sometimes called the "King of the Jungle" but not because anyone looked at him and mistook him for an actual king.