The Grey Knights


 * Their real name is Palatial Guard (a.k.a.: paladins). But most people just call them Grey Knights.
 * The name Grey Knights comes from the distinctive dull grey plate armor they wear.
 * They are trained to resist possession and magical spells.
 * They are all magically adept. In order to join the group, they are forcefully subjected to demonic possession. If they are able to fight the demon and cast it out on their own, they pass the test. Otherwise they are killed on the spot.