The Elements existed long before anything else. They built the world, populated it through intermarriage(creating the first Mages), and guard it in a sense. They take a form like humans, though they do not usually interact with them.
Long ago, Spirit and Void had a quarrel. Spirit won, consuming his enemy. All of Void's offspring died when he did, and only those who can use the Element of Spirit can wield Void. Since the story of Void is one of violence and death, Void can only be attained by murdering another Mage.
Since that time, Spirit has been making plans to allow the Mage bloodlines to fail and take over the world.