S.T.A.L.K.E.R.
S.T.A.L.K.E.R. is a name of series of popular PC games (Shadow of Chernobyl, Clear Sky, Call of Pripyat), in which many fractions of people called "S.T.A.L.K.E.R.s" are waging wars for a land around Chernobyl nuclear power plant (AKA the Zone), which hides artefacts with weird physical properties. These artefacts are extremely valuable.
The acronym S.T.A.L.K.E.R. stands for:
Scavenger
Trespasser
Adventurer
Loner
Killer
Explorer
Robber
That is really a good
description of what most stalkers really are, although the acronym only makes sense in english.
The difference between S.T.A.L.K.E.R. and stalker is that
one of them is a job and the other one is a mental sickness.