The Martyr of Draegan is a rare enemy only appearing during the Draegan fight. It's a cultist with a black robe and a white belt, holding a bomb.
These enemies will always spawn around Draegan and will immediately attack you. They begin to spawn only when Draegan is in his Awoken Form (2nd phase of the fight). When they're close to you, they will explode, dealing easily more than 60 damage, but dying in the process. To avoid being hit, the player has to kill them with ranged attacks before they come too close.