The Guard, is the title of the ruler of the Valley of Shadows. The guard has incredible powers sustained by the valley's prisoners. He and the prison exist by absorbing the life force of the prisoners and so the captured creatures remained petrified for most of their time.
The current Guard intends to absorb the light of Meridian's power and with it, all of the magic world's life force.
Caleb confronted the Guard and managed to somehow defeat him.
As it turns out, the guard is revealed to be just another prisoner. The only way it could escape its role is to be defeated and hence the victorious challenger became its successor.
Caleb undergone a metamorphosis that weakens him for a while. The original guard then escaped bringing along him the Guard's Lance and the Blue Destiny.
He was about to escape when Caleb appeared and retrieved the objects resulting to the guards perpetual petrification.
It is unknown whether the guard was the original or just another challenger who managed to defeat a guard.