I really like my NPC's, in very simple terms. They've developed in other games and they have certain interesting character traits that bring the game alive for me and, hopefully, my players. I've created two sheets for my major pair of them. The players will usually be dealing with one or the other, though there's a certain amount of friction between the two.
Anjya is, secretly, a worshipper of Khaine, the god of murder. The PC's will notice, as time passes, a string corpses killed in ritualistic fashion following them on their travels. While they might beleive the culprit is one of the many Chaos worshippers in thier midst, Vostrachen is sure to pick up the peices, eventually. He'll pick them up that little bit faster the more the PC's go whinging to him to sort their problems out. (Vostrachen is a previously discussed witch hunter of Verena, scary, but still capable of assisting in his own way.) If the PC's put the facts together first, they can convince Anjya to give up worshipping Khaine, she only did it because he (seemingly) answered her prayers to assist her in murdering her father. If the PC's help her get her revenge, she is much more likely to give up her heathen practice.