As you play, you come across many of these artifacts. Those who enter the Zone specifically in search of these artifacts are known as stalkers, hence the name of the series.
Due to the destructive events caused by the nuclear reactor disaster, mutated humans and animals began springing up - along with artifacts, which are known for giving special powers like stamina regeneration or radiation reduction.
The Stalker series takes place around the Chernobyl Exclusion Zone, with each entry focusing on various characters trying to survive after the catastrophe.