Find Borelgore in the northern wastes of Eastern Plaguelands and destroy him. Return to Nathanos Blightcaller when the mission is complete.
Past the Argent Dawn encampment of Light's Hope and west of Northdale, you will find the corpulent maggot beast, Borelgore.
I've lost entire regiments to that monster. His size knows no bounds! The more he eats the greater his girth becomes...
While I would not suffer any emotional harm should the beast devour you, I would prefer that you were the victor. I recommend you enlist the help of others for this mission. Borelgore has been known to devour small battalions foolish enough to attack him.