Stalker

is the one who follows another one or "thing"
could be animal or human to achieve something that always wanted and for personal interest also that thing
could be
killing
stealing
kidnapping...etc

the most sensible examples of this are
Predatore "movie"
and the game "s.t.a.l.k.e.r"

I think he is stalking me!!
look! do you see that man over there!!! he is a stalker.

by S.T.A.L.K.E.R November 23, 2008