Opposite of a 'terrorist'.
Modern day cops and robbers, it's the counter-terrorists job to take down the 'terrorist'.
Good example's of counter-terrorist groups would be:
All groups seem to operate on the same modus operandi. They basically seek to maintain national security and kill the bad guys quickly and swiftly when they decide to rear their ugly heads and do something stupid like attempting another suicide bombing <except in Scotland where terrorists need to be protected from the civi's).