God's Demon by Wayne Barlowe
''The powerful Lord Sargatanas, Brigadier-general in Beelzebub’s host, is restless. For millennia Sargatanas has ruled dutifully over an Infernal metropolis, but he has never forgotten what he lost in the Fall. He is sickened by what he has done and what he has become. Now, with a small event—a confrontation with a damned soul—he makes a decision that will reverberate through every being in Hell.* Sargatanas decides to attempt the impossible, to rebel, to win his way Home and bring with him anyone who chooses to follow...be they demon or soul.
He will stake everything on fighting all the abominable forces of Hell arrayed against him, when the prize is nothing less than redemption.''