EXCELLENT questions, Winter.
I was raised in a Christian household, and I was exposed to the idea of the 'devil' from an early age. The idea that Lucifer's pride condemned him to as eternity of darkness struck a very strong chord, and the influence of that idea is VERY prevalent in all of my books. Pride is the enemy of Love. Love (God) is always there, but we must choose it. To choose it, we must forsake pride.
Wrothgar is simply an embodiment of all who would lead others astray from light and enlightenment. He represents pride, delusion, ignorance, arrogance...the elements that make one vulnerable to Darkness. He is NOT the ultimate evil in the Universe--there's no single embodiment for that.
The Asari are like angels in some respects. Kotos is probably the closest thing to a 'Satan' figure...there's an anthology of short stories about to be published featuring one of mine--The Unbroken Mirror--which deals with the downfall of Kotos. (If you like Alterran history, it's a corker!) I was asked to do artwork for the cover and illustrations for the inside. I'll share when the cover's done.
As for other influences, I'm sure there are plenty (I might not even be aware of some of them). When you get to the ending of Ravenshade, you'll understand.