Maglubiyet rules over both goblins and hobgoblins, allowing other gods of the pantheon to focus on one race or the other. And Khurgorbaeyag is the specific power of goblins as a race, the leader who bows only to Maglubiyet. It's Khurgorbaeyag who rigidly drives the goblins to the atrocities they commit in war, and Khurgorbaeyag who urges them to take loads of slaves to do the work the lowest goblin would scorn. His priests are his highest servants, and he uses them to push the race in the direction he wants it to go.
Khurgorbaeyag obeys Maglubiyet mainly because he's seen what happens to powers in the pantheon who get too uppity. Still, in his secret heart, he plans ways to depose the tyrant ruler. However, until he has a foolproof plot, he remains as loyal as possible.
The Overseer also has a rivalry with Nomog-Gaeya (the god of hobgoblins), for he knows that the race that succeeds the most is likely to curry favor with the head of the pantheon - and he's determined to have his goblins climb to the top of the heap. Finally, Khurgorbaeyag has established an alliance with the bugbear power Hruggek; the two of them sometimes work together against the lesser orcish powers.