"He marches forth in the holy, metal raiment of the Kasaphescence, ready to lay down his life in the name of his Argent Fathers."
Usually seen at the final level of Bethesda Susa, guarding the holy place with a religious fevor.
They can be somewhat difficult to deal with, but shouldn't pose much of a problem for most characters. But you should be cafeful because their blocks can cause you to stun.
They might sometimes have better or different equipment.