Formerly known as Atarus, a member of the Eighth Circle of the Varanguard, Eternus renounced his service towards Archaon and was thrust into the lightning-wracked region known as the Cursed Skies, trapped amongst the swirling souls of Stormcast Eternals unable to return to the realm of Azyr. Revived by Be'lakor, his burned form was infused with the souls of these Stormcast Eternals, given new life by the very black lightning which tormented him for eternity.
Age of Sigmar
Eternus serves the agendas of Be'lakor, working tirelessly not to fail his master, lest he loses his gift of immortality. Currently, he is furthering a secret agenda by Be'lakor to usurp Archaon in his position as the Grand Marshal of the Apocalypse, employing spies and covert agents, such as the Chaos Legionnaires.