Who controls the monolith? (S.T.A.L.K.E.R.: Call of Pripyat)

As you know monolith brutal psycho-killer, etc. but in one quest they were normal and was asking that something or someone controls them. so who was it? And in one quest they were in a trance, sitting near a pile of garbage and so them someone contacted. In the game a clear and precise explanation I have found. can who-thread knows? or let us lay out his thoughts on the matter: