I'm thinking an Inquisitor loosely based on the comic character Deadpool could be alot of fun. Deadpool will frequently "talk" to a voice inside of his head. In fantasy RPG terms, maybe the voice inside of this character's head is the voice of his god? Is the voice inside of his head really the voice of his god, or is the character just crazy? Who's to say?
Now I wouldn't base this character 100% on Deadpool. You don't have to be quite as looney and manic as Deadpool, and the humor can be toned down, since DP is VERY over the top to the point of being extremely cartoonish. You don't have to play your character at anywhere near that level of lunacy. But DP does lots of grim things while not being very serious. So using him as a rough inspiration while still making your character fit your world and campaign could be interesting.