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.
She looks like a warrior. I mean Bellatrix does mean warrior. And she's also a bit of a fatale. She's the right hand of Voldemort and the only woman death eater.