Wargs are to wolves what lions are to cats: bigger, stronger, and always hungry. Wargs tend to hunt in packs, and seem to feed off the fear of their prey as much as the meat. This pack mentality also makes them the target of various training programs, which tend to be successful some of the time. A warg will never serve well as a house pet, but they take to being war animals with relish.
Since warg breeding lands tend to fall under the dominion of the Orc Lord, these creatures are associated with that dread Icon in the eyes of the common folk. Wargs also just don’t seem to like humans ever; there hasn’t been a single instance of human trainers ever successfully taming a Warg. Because of this, Imperial policy about wargs is that the only good warg is a dead warg.
Icons: As has been mentioned, most wargs live in the Orc Lord’s territory, and so most trained wargs tend to be in the Orc Lord’s army. That said, some wargs are trained by followers of the Diabolist or the High Druid. There are also feral wargs who don’t follow any Icon but their hunger.