[khorboth]

I really liked The Master from classic Dr. Who. He had his own agenda and didn't care who got hurt in the process.

The key was not caring. If it was easier to not hurt people, he didn't hurt them. If killing was easier, people died. He didn't care about The Doctor (or anyone else) except as their status as help or hindrance toward his objective.

This meant they occasionally worked together, and sometimes worked at unrelated things near each other. And betrayal was not a given. If it wasn't in The Master's best interest, it wasn't going to happen. It wasn't until later that one of his objectives became the elimination of The Doctor who was a frequent obstacle.

This kind of indifferent superiority and calm calculation made him very chilling.