Dogretch

Horned Devil whose goal in life is to kill the Succubus, Pencheska Natyssa.
Dogretch was rescued by the party in Siege of the Gnoll Rock Fort: Game 2 and The Devil's Rescue: Game 3. 
He was captured by the Arithmós Necromancers of the Order of the Necromantia that were using the devil’s blood as part of their recipe to infect birds, gnolls and humans. An infected creature can provide an evil mage the ability to scry upon the diseased (specifics unknown), and their body is slowly consumed by black acidic ooze until the explode harming all around them.
Dogretch was in a basement were crates, bottles with black liquid, spell components.
In the basement, there was a pentagram circle with five burning candles which are flickering and ready to go out with Dogretch chained to the floor with a dozen metal knives with blood draining into cups outside of the circle.
The party interrogated Dogretch, eventually agreeing to let him go free in exchange for his killing the gnolls.
Dogretch lived up to his side of the bargain, laying waste to and murdering the gnolls, mostly women and children.
Dogretch wants to finish his quest to kill the chaotic evil succubus so that he can return to Hell's sixth and seven planes, and engage in orgies with evil elves.