Terrorist/paramilitary group in Colombia. A far-right group. The acronym is for United Self-Defence Forces of Colombia. The group's only reason for existence is to assassinate left-wing rebels and especially people suspected of sympathising with them or of struggling for social improvement. This group murders thousands of peasants, trade union leaders, human rights activists, liberal and left-wing politicians, etc., every year.
They wear what they call "the mask of the executioner", but apart from that, they are mostly regular Colombian soldiers and are effectively the dirty tricks wing of the Colombian army which covers for the government and its US allies because they can disavow responsibility for AUC atrocities. The current president Uribe is a close ally of AUC and has hired them in the past.
Although AUC are major drug traffickers and closely linked to drug barons, and are also on the US's terrorism watch list, they are indirect beneficiaries of the US intervention in Colombia, which is directed mainly against left-wing rebels.
AUC troops have recently turned up in various incidents in Venezuela, on the side of the reactionary opposition movement.