I have this character who I'm beginning to think of in terms of archetype: Mastermind, Master Manipulator, whatever tongue-in-cheek role you want to call him. He's the guy behind the scenes, he may or may not have some sort of upper employer, his motives are never (entirely) clear; simply, he's an enigma. The writer leaks a little information about him over the course of several books or installments. The best example I can think of is the G-Man from the Half-Life computer games (shame I can't remember a literary example). My question: How much about his motives do I need to know? Let's say it becomes evident that he's trying to destroy a certain faction/sect/society. Do his motives need to be deeper than that? He gets little actual screen time.