(appropriator is a kind of ...) a person who acquires something (usually permanently)

• acquirer

(... is a kind of appropriator ) someone with an irrational urge to steal in the absence of an economic motive

• kleptomaniac

(... is a kind of appropriator ) someone who hunts or fishes illegally on the property of another

• poacher

(... is a kind of appropriator ) someone who acquires land by preemption

• pre-emptor
• preemptor