Spoiler Warning! In the early days of exploration in the Zone, those who would eventually come to form the Monolith were Stalkers like any other Stalker. However, as they spent more and more time ...

There's a hard-to-reach Stash by the Cafe located in River Port POI in the Pripyat region of Stalker 2: Heart of Chornobyl, ...

Matter of Honor side quest involves Skif helping a bunch of wounded Duty soldiers fight off a Monolith attack in Stalker 2's Cooling Towers region.