Apostle

An Apostle (sometimes also referred to as Acolytes) is a mortal that has been granted eternal youth by a Dark Lord in exchange for servitude.

An Apostle is created via a blood pact, the prospective Apostle drinks the blood of the Dark Lord, and if he survives he is rendered immortal.

Features
They do not have full immortality, the lack of an Invincibility Field means that they can still be killed through regular means like murder or suicide.

Apostles have much more potential than regular mortals.

Like how the Dark Lords must obey the Demon King, Apostles must obey their Dark Lord.

A Dark Lord can have an infinite number of Apostles, but the more Apostles a Dark Lord has, the weaker he becomes and the less control he can exert over his subordinates, this isn't a problem for Dark Lord Kesselrink as all of his apostles deeply care for him, allowing him to have eight.

Even if the Dark Lord is destroyed, the Apostle remains.

If the Demonic Blood Soul of a Dark Lord is consumed successfully, the new Dark Lord inherits the Apostles of the last.

Dark Lords can revert their Apostles back to mortality at will.

Purpose
Apostles are typically used as combat personnel for the Dark Lord, so they don't have to dirty their own hands.

Sometimes they're made to take care of the Dark Lord and his properties, the Vampire Maid Apostles of Kesselrink tend to him and his estate.

Sometimes they're just made to be pets, Kaybnyan and Kaybwan fit this role.

Lesser Apostles
This is a term given to people who are working with Dark Lords under good faith, no blood pact.