When Agamar (the sorcerer who brought life to The Vortex) created the portal, he wanted a way to ensure that life would keep thriving. He didn't want it to go back to the desolate place it had once been. So, once the land was filled with life, he used the portal and his remaining life force to summon/create a group of guardians. These immortal beings would all represent some aspect of life, ensuring that it would continue long into the future. Guardians of both good and evil were created, their purpose to maintain balance. 

They are the only beings allowed in/able to enter the sacred site of The Vortex, the place where they hold council meetings and recharge. Though immortal, they have to make trips back to the site to recharge their energy. 

Guardians are of various qualities, elemental, emotional, ideas... etc. Similarly to the gods of Greece, they quarrel and fight amongst each other, but that's part of life. There is harmony as well as strife, peace as well as war.

Those posessing great skill and capability may be appointed the title of "Minor Guardian."  Though not immortal, they share in the great responsibility of mainting balance in the world.