In Killzone 3
The Capture Trooper is a Helghast soldier that the player fights in Killzone 3. They use wrist blades (Retractable Knife) and prefer to sprint at enemies, unlike most Helghast who shoot from afar. The Capture Trooper also has armor which allows it to take in more damage and have an opportunity to survive. They usually go in pairs, and go for the kill. It is easy to realize that there is a Capture Trooper by hearing there panting noises, and will sometimes say 'I kill you!'.
There is an achievement 'Turn the Tables' which to earn it, the user will have to melee kill a Capture Trooper
In Uncharted 3 multiplayer
The Capture Trooper appears as a multiplayer skin on the villains side in multiplayer. It is available in Game Of the Year Addition or from a special offer at GameStop.
Note as well, the armor is purely cosmetic, and does not affect the player, and the knife cannot be used.