Havel "The Rock" is an iconic character who had appeared in all of the Souls games- at least, his knights do. Havel was known as the high bishop in the old "Way of the White" covenant, serving under Lord Gwyn- the final boss of the first Dark Souls games- as a faithful asset. He is well known for hating magic and once made enemies of a dragon named Seath the Scaleless, although the dragon only appeared in the first game.
Havel is a bishop who has long since become hollow, although his armor, forged out of solid stone, and his dragon tooth hammer are still in the world as of Dark Souls 3. Even though the enemy donning Havel's armor appears as Havel, the same can be said for the similar enemies in the two prior games, indicating that this may not be Havel. None the less, with a nearly-fatal move set and tremendous magic resistance, this is not an enemy to be taken lightly.