Shamans usually try to gather power out of altered states of consciousness, often in order to interact with the spirit world. One of their goals could be to direct those spirits or transcendental energies into the physical world of wasteland. Be it for healing, divinatory or more obscure purposes. They also seem to have special connections to animals and plants. And to this point, a shaman has been the only character who actively and willingly managed to use a portal.
g8s was the first shaman in the wasteland collective, and mentor of s33k3r who is now holding up shaman practices on her own.
But it is not unlikely other shamans are to be found somewhere in wasteland.