Lost Scrolls : Skyring - The Only Spirit Bender

Could it be someone could be greater than the Avatar? Is it possible that someone hides, a person so legendary that only lost scrolls write about? Aang is learning water at this point and going to move on to earth next but danger far more extreme lays in his way, sure his powers are so rare that only one person every generation in the entire world has them but could this be enough when things beyond physics start occuring? Or will he need someone, prehaps a person who can do things unknown to man, but will the person's dark side take control before it can become light?