Sounds like Morghur was a walking waystone/herdstone experiment that got corrupted.
Maybe Morghur was something like the earth elemental in Karag Mhonar, a long forgotten magical collaboration between the Dwarfs and Elves.
The throwaway exposition by Asarnil was a hint, as it suggested the High Elves had ulterior motives to help take down Morghur.
The thing is a living incarnation of Chaos and the ur-beastman. No one remotely sane needs an ulterior motive to kill him.