Necromancers do not have a formal organization or guild. They are individuals with magical talent who, for one reason or another, have begun studying the most forbidden of arts. They are fascinated with the forces of life and death, as well as what makes living (or unliving) bodies function. This kind of magic is highly forbidden, and necromancers must practice their art in places where they will not be discovered. Plague districts and hidden crypts are common places for them to congregate.
Not every bored youth with an interest in pulling wings off of birds becomes a necromancer. True necromancers have studied life and death for years, ritualistically slaughtering and dissecting all manner of life to learn how it works. Necromancers can learn from books just as Mages can, but they learn more from active experimentation than isolated study. For this reason necromancers are always interested in obtaining the bodies of the recently dead or dying. They have been known to purchase corpses from disreputable surgeons just as anatomists do. Though anatomists are mainly interested in improving treatments for disease and injury, they do share an interest in dissecting the dead. Cooperation between the two groups is not unheard of.
A skill eventually learned by necromancers is how to reanimate the bodies of the dead. When necromancers animate a corpse, they do so by infusing the corpse with a small amount of their own life force. Usually this just weakens the necromancer for a time, requiring them to rest. If a necromancer makes a mistake, however, or if they are just unlucky, the loss is permanent. This results in necromancers slowly loosing the use of various limbs and organs. The longer you use necromancy, the more likely you are to have paralyzed limbs, blind eyes, or rotted tongues. Sloppy necromancy takes a high toll. Older and more powerful necromancers are often shrivelled and rotted--and occasionally mute--from extended use of their power.
Necromancers frequently sacrifice everything to perfect their art. Their health, their happiness, their dignity, their humanity, all fades away in the pursuit of that which seperates life from death. They're emaciated, weathered and aged, festering with diseases earned from playing with rotting organs and bodies....which in turn their magics feed upon to extend their lives to untold lengths. It is not uncommon for necromancers to live for centuries.
Because Necromancers deal with both the dead and undead, they invariably come into contact with evil spirits. It is common for Necromancers to become corrupted by these spirits (as if they were not corrupt enough to begin with).
Relationship with Other Factions
Necromancy is, of course, highly against Church teaching, and engenders fear and disgust in virtually everyone. Even other Mages are publically opposed to it, though it's not unknown for some to dabble behind closed doors. Necromancy is a major sin according to the Builders, punishable by torture and death.
Many rumours exist about the Inventor's Guild using necromancy in the creation of their automatons. There is no evidence of this, however, and the rumours are vehemently denied by the guild.
Powerful necromancers are very rare. Necromancers in general don't congregate with each other; their work requires solitude (and they tend to be anti-social to begin with). Any group of necromancers is likely to be small, and full of amateurs.