The demon Wa-Lee The Solicitor is the boss encountered in the Demon World.
The worst demons are those who speak. The Solicitor is one of those entities that you could only pray to never encounter. A being of ancient power, he is the one who oversees the fulfilment of demonic contracts signed by various foolish mortals. He has a symbiotic connection to the binding force of those contracts - while he protects them, he can also channel the power they provide. This allows him to call upon them in time of need, making him a resourceful and crafty opponent.
"I have no quarrel with you, mortal.
A pact is binding for both sides and the price must be paid, one way or another."
- - Wa-Lee The Solicitor