Anti citizen is a term used by the Combine to designate a person as a threat to their control. The Combine use the term 'anti citizen' because the behavior of Anti citizens is the opposite of that of citizens (or at least, the Combine's definition of a citizen as a person under their rule who does not resist them). Each Anti citizen is given a number representing how dangerous they are to the Combine, and ranked in descending order. Gordon Freeman is Anti citizen One, and thus the living being who poses the most danger to the Combine. However, in Nova Prospekt, the dispatcher addresses the player as "Anti citizen Freeman", which leads to speculation that Anti citizens are designated not only by numbers. Anti citizen is a probable Combine synonym for "Public Enemy".