He's really sort of the devil. He's completely emotionally detached. He has no empathy. You find that in psychopaths. It's about power with Voldemort. It's an aphrodisiac for him. Power makes him feel alive.
“Wise anger is like fire from a flint: there is great ado to get it out; and when it does come, it is out again immediately.”
“Don't walk behind me; I may not lead. Don't walk in front of me; I may not follow. Just walk beside me and be my friend.”