The Book of Exalted Deeds offers the Saint template for good-aligned characters. This template is quite powerful, but has strict prerequisites (as described in Sainthood section).
Is there any equivalent template/prestige class designed for evil heroes and villains? I am looking for something official that can stand against a Saint character. Beyond powerful mechanics, I am looking for something like a good background/prerequisite/sacrifice (similar to the Sainthood section of the Saint template) and suitable powers for the chosen of a god.
I am looking for something more the evil version of the Saint. My gaming group has a Saint character and I am looking for something that would represent the evil god they are fighting. They are fighting the god's minions (god of undead) and I am in search for a NPC suitable to be the leader of the minions. Also, the group must realize that the NPC is something like the Saint in their group: the chosen champion of the evil god.