Orcs are dystheists. They believe that gods are apathetic at best, and blatantly hateful at worst.
Orcs are the great iconoclasts. The soft, human gods are either powerless or great destroyers of the orcish race. After a warband conquers a city, each orc will relieve themselves in the largest temple.
The gods of orcs are either ignored or hated. (Orcs aren't big on fear, even when they should be.) They aren't worshipped. They are appeased. Or they are bargained with, like merchants in the marketplace.
This is why orcs portray their gods as ugly as possible.
When you see a group of orcs chanting in one of their temples, they are not scared or reverent. They are angry, because gods are the only opponents that cannot be cut with an axe.
Temples make orcs angry, and anger makes orcs want to kill something. And even the apathetic gods, who can sometimes be reasoned with, are only ever asked for prowess in combat, because nothing else is worth praying for. Nothing else is worth making the promises that gods demand. Blood for the blood god. Skulls for the skull god.
And so all orcish gods loo like war gods to outsiders.
ORCISH PRAYER TO BE IGNORED
This one is small.
His bones creak in his sleep
and his marrow is sour
and full of hatred.
He is wretched
and not worthy of anything.
ORCISH PRAYER AFTER A BATTLE
Blood feeds the hungry earth.
Blood makes the grass grow green.
With blood I have washed your face
and your dogs have lapped it up.
Now leave me alone.
Orcs hate their gods almost as much as they hate themselves. This is because the gods hate them. They believe themselves to be cursed: with stupidity, with ugliness, and misfortune. How else could they continually lose wars to those who are so much weaker than them?