The Great Guardian, also called the Grand Guardian (대호법) in the manhwa, is a position handed to the Great Guardian Family that serve as the "shadow" of the Lord of the Heavenly Demon Divine Cult. Aside from being guardians of the Lord, they also monitor the Lord to ensure that he doesn't violate the Heavenly Demon's Order.
They are one of the highest authorities inside the Heavenly Demon Divine Cult and the only ones allowed to bring their own weapon inside the Great Hall of the Lord's palace. It is said that the Great Guardians are stronger than the Lord in order to protect the Heavenly Demon's Order since they are taught personally by Cheon Ma and his martial arts.