Etymology of the world "Tool"

[Malachii]

My fellow 2+2ers...

I have to confess, when you call each other (or others) a "tool" I have absolutely no idea what you mean by this. Obviously, I'm able to infer that "tool" is some kind of insult, but why call somebody a tool? Why not call them a bozo or a "moran?" When did we start calling each other tools? I personally have always felt that Tool is an excellent band, perhaps not as good as A Perfect Circle, but...

If someone could kindly fill me in, I would appreciate it greatly.