Way of the Wicked: Revenge of the Forsaken
The Ninth's Daemonic cohort
It turns out that Grumblejack hails from a race of daemonic ogres set to protect the Horn of Abbadon a long time ago while the death cult still inhabited it. The Ninth found a way to transform Grumblejack to a more daemonic form. For this Grumblejack has sworn alligience to the Ninth for as long as he lives.