Faust
Faust grew up the son of a Paladin. Intrigued by the divine power his father could evoke Faust started to follow in his father's footsteps, trying to learn how to evoke the same powers of protection and defence. When coming of age, Faust saw his first battle; although only a skirmish, he was repelled yet compelled by the violence, the mayhem, the power. The lure of the dark path of shadow magic was too tempting to resist, and Faust secretly started studying it, learning new ways that were orthogonal to those of his father's.
Knowing that his father would not only disapprove but also try to stop him from learning this magic with force, Faust took on his new name, dropping any ties to his family in the process, and effectively disappeared from their view. His skill in the dark arts grew to the extent that he became capable in small fights, at which point he joined the ranks of the Alliance. Faust did this partly to gain more training, partly in a hope to attone for what he saw was letting down his father, but partly just to fight, to kill.
Faust enjoys the battle for the sake of battle, for conjuring up dark spirits to use as his own. Whilst fighting for the Alliance, he secretly hopes that the battle will either last for his lifetime, as he knows his kind won't be tolerated once evil has been defeated. And while he has no bond to the evil creatures he fights, he respects them for their power and wonders if his spirit is strong enough to resist switching sides should the fight go against his Alliance forces.
Only time will tell.