Firefly

(...)

10. The Reavers - Serenity

The Reavers themselves weren’t that scary, but they become gain a lot of terror from the way the rest of the world fears them. They are the only creatures I know that can make Captain Mal shake in his boots. And shake he does when he orders the town to lock themselves in a bank vault until they run out of air.

(...)

Click on the link for more :

http://io9.com/5392116/1+10