Vashtorr

Vashtorr the Arkifane is a daemon unaligned to any of the Chaos Gods who holds dominion over the Forge of Souls; though he has no loyalty to any of the four major Chaos Gods, he has established himself as a demigod by acting as their shared arms dealer. His technological skills have made him not only a figure of adoration among the Dark Mechanicus and Warpsmiths among the dark powers, but also the mastermind behind the newfangled Arks of Omen, weaponized Space Hulks that are part of Abaddon's renewed offensive on the Nachmund Gauntlet.

While holding considerable power in the Realm of Chaos, his efforts to become a fifth Chaos God have so far been stymied by a lack of influence over the Materium, and so he sees his alliance with Abaddon as an opportunity to establish himself in realspace. Thus far, the only real opposition he faces is from Be'lakor, who undoubtedly does not like the competition for his own attempts in ascending to godhood.