Merlin tried to bring order to the troubled land of ancient Britain by providing a king from the Uther Pendragon line of royalty. By enchanting Igraine to see Uther as her husband, Arthur was engendered. Later, Uther married Igraine, before Arthur was born. Uther, however, was not to have a son to enjoy, for he had agreed with Merlin to do anything to have a liaison with Igraine for one night. Merlin's price was the son born of the liaison.
As an archetype of mythology, Merlin developed from Trickster, to Magician, to Oracle, to Sage (the four levels of development discussed in Jeff McBride's Magic and Mystery School.