Destiny

Destiny is the thing that a person has to do to fufill it.

Known Destinys:
 * Merlin: To aid King Arthur to unite the land of Albion.
 * Morgana: To bring back the old ways.
 * Arthur: To unite the land of Albion and become the greatest king the world has ever known.
 * Mordred: To kill King Arthur.

Creatures capable of knowing ones destiny:

Kilgarrah has the ability to know someones destiny and does his best to help Merlin fufill his. It is unknown if all dragons have this abilitybut you may find out in Series 5.