The Bastard is a creature from the Mythos. Half Were, half GOO minion, it was apparently formed during the war that predated The Sundering, and was involved with that spell. It is currently residing in the Sierra Madre Mountains in California, and is building an army of corrupted weres (part human, part were, part GOO essence - nicknamed "Voodoo Wolves" by Jericho) with the intention of eventually repeating the spell. However, as of December 2006 it is not ready to enact the spell as it needs lots of "gifted minions" to accomplish the spell, and a large blood sacrifice to make the magic work.
Its current modus operandi is to use the Voodoo Wolves to attack Were tribes. The venom and claws of the Voodoo Wolves contain a retrovirus which quickly (over the course of a few hours) transforms the victim into another Voodoo Wolf. So far most of the were tribes in the Western US have succumbed, and as of December 2006 it has turned its attention to the Medawihla Reservation. It is particularly interested in these Weres as they are direct descendants of Garrand, the Champion of the West in the Five-Fold Court. It is also very interested in killing Fey, as it is annoyed that Aunghadhail wasn't completely destroyed in The Sundering.
It currently appears to be in a temporary alliance with The Necromancer - however, as the Necromancer intends to thrall Fey rather than kill her, before using her power to aid him in killing The Bastard; it's uncertain how long this alliance will last.
Its physical appearance is unknown, but is probably similar to its visage in Dreamscape, where Aunghadhail/Fey met it while recovering from one of the Voodoo Wolf battles on campus: a writhing mass of familiar creatures' bodies, tentacles, and unspeakable foulness.
Wyatt Cody sees it in a mystic dream as "The ground shook, drawing his gaze to the horizon where some horrific thing could just be made out, bloated body the size of the Astrodome, with flaying tentacles, bat wings and a sense so horrifically unnatural that for a brief moment he felt his mind despair."