Molydeus

Monsters. They make Balors look like children in comparison. I've heard of them being killed but... it ain't somethin that happens regularly.

Molydeus are the right hands of Demon Lords. One exists for each Demon Lord, no more and no less. They exist to protect their masters and they are each unique in the weapons they carry, mimicking their masters. A Molydeus can easily dispatch a Balor or any other greater demon, which is why they guard the secret to their master's life force. Each possess a cameo of their Master that they are charged with protecting. Unless the Cameo is destroyed a Demon Lord can not be killed permanently.
Molydeus possess two heads, one of a wolf and one of a serpent. The Serpent head is linked to their master so that they can see what their servant sees and speak to it from afar. Should a Molydeus turn from its master, it will be hunted down by the Demon Lord in question and killed if it cannot best its master. Each Molydeus carries a weapon that mimicks its master's weapon of choice and influences its abilities.