read up the stones that are placed in plains. One of them explains pretty much everything about Yagluth and fulings.

As i understand it, the lore more or less states that Yagluth was a wizard/shaman king to his people the fuhlings, and having challenged the gods and failed was torn in half and cursed with undying. If nothing else you could see him as a prelude to the introduction of magic in the following biome.