One idea I've thrown around in my head is an Orc who has made a deal with demons for the promise of more power than any Orc warlord before him. In exchange he has promised whatever demon lord he has pledged himself to a ridiculous number of souls, and to do that he required a large number of sacrifices, which means a lot of nasty evil priests.
This Orc is cagy, and more cunning than his kin. He devised a way to turn his army into a roving horde of rampaging demonic priests. Their "right of passage" is an elaborate ritual that completes with a sacrifice, and an oath of fealty in a language that the Warlord calls "true orc" (Abyssal). Their weapons are blessed by the Warlord's high priests (either demons in disguise, or Orc shaman in on the real scope of what's happening.)
To build this army, he either murdered (by his own hand, or through another) all of the various leaders of the surrounding Orc tribes. He then consolidated his power and took them over one-by-one, crushing any opposition.
As far as crunch goes, I imagine a Bloodrager from the Advanced Class Guide with the Abyssal bloodline. He'd be potent on the battlefield, and if you need to give him an extra boost, there are quite a few Demon Lords that hand out some pretty scary boons. With the amount of sacrifices he's making, demons will be begging to court him. He might even be made into a half-fiend.
