Guardian Angel is a being that takes the the normal form of an alicorn, formerly a part of the Celestial Guardians. Her true form, however, is unknown.
It is unknown what her history is, or even her true name. However it is known that she was at one time a Celestial Guardian, who eventually left to persue her own goals. She had not been seen again until she assisted Lightblade on his journey to defeat the Darkness. It is also unknown what her true motives are, but at the time being, it seems that she works to guide important characters who would determine the fate of the world.