The Warhorde Of Eternus can be built so that it serves Be’lakor or Archaon depending on which miniature you choose to lead it. You could always build Eternus, Blade Of The First Prince or you could just make a generic Chaos Lord On Daemonic Mount and carve out your own story in The Mortal Realms. Your leader is then joined by Ogroid Theridons, Chaos Knights, Chaos Chosen and ten Chaos Warriors.