The Klu Klux Klan (KKK) are a group of racists who target minority groups, particularly those of afro-caribbean origin. You first encounter them when working with Eliza Jackson and Big Man at Northside during the first campaign.
Their melee troops tend to be weak but numerous, mere cannon fodder to divert your attention from their ranged attackers who are much tougher to deal with. They occasionally also use talents such as Distract, Fire Bomb and Second Wind.
The KKK are based on the real life group of the same name, The Klu Klux Klan.
They are still active in modern day USA, where they are increasingly aligned with neo-fascist and neo-nazi groups.
In November 2014 they threatened to use lethal forceagainst protestors and members of the hacktivist collective Anonymous who were protesting against police brutality in Ferguson. Anonymous successfully 'removed the hoods' of several KKK members, finding that they had strong ties to the local police.