For some people, it takes feelings to fight. It helps give those people the necessary motivation to, you know, fight someone.
Others have no such requirement, and in certain cases, those are the scariest ones. Think back to Hannibal Lecter, Anthony Hopkins' evil genius character from The Silence of the Lambs, who ate everybody's liver with fava beans without his pulse ever rising above 85 beats per minute.
Then, of course, there are unemotional fighters who are just plan, old boring people.
These are the least-emotional fighters ever. Each guy is either scary or boring. I'll let you guess which one in each case.