What are we? We are Scavengers, Trespassers, Adventurers, Loners, Killers, Explorers, and Robbers.

"Stalkers come to the Zone for a number of reasons. Some go for profit, some for adventure, some seek to
get away from the world, to escape law or personal problems. It follows that former criminals can be found in all of the stalker factions except Duty, though most criminals not part of a bandit clan have long since started new lives." (http://stalker.wikia.com/wiki/Stalker)