User blog comment:Chaosian/Poll Results 19 - Why is it that you like Metro 2033?/@comment-1403643-20120129224328/@comment-4488593-20120130153514

Aliens are in Roadside Picnic, they created the Zones. S.T.A.L.K.E.R. was influenced by Roadside Picnic. That's probably where he got aliens from.