What are some logical reasons as to why the Iron Giant may have been sent to Earth?

The WB's sleeper classic The Iron Giant is probably one of my favorite animated movies of all time, and because it's a family film I understand and accept that there is a heavy film of intentional obscurity about the giant's true purpose. Indeed, I doubt the creators ever settled on what his trip to Earth was actually intended for. Nevertheless, since the last time I watched it with my kid, I've thought about it a lot... and would like to take it to an audience to discuss and pick apart various blind spots in my hypotheses and hear some that I maybe haven't considered.

My first and predominant theory about TIG is that he is a kind of super-advanced AI probe,- this would explain the metal-eating, as metal is neither combustible nor radioactive, so he can't realistically be using all the metal he eats in the film as a fuel source. So why is this normally passive probe equipped with WMD's? I think whatever species that sent him to Earth are probably pragmatists. They don't necessarily want to harm other life, but perhaps if the planet has enough of the resources that they need (metal, probably) they will then decide whether or not to colonise the planet or at the very least, harvest it's resources- likely with plenty of interspecies bloodshed in the meantime. If the probe doesn't find anything valuable, then they will simply move onto the next planet. However, being pragmatists, they probably realise that should humans notice the probe, they probably don't want us to capture it and reverse-engineer it and perhaps ultimately use their own technology against them, and so the ordinarily passive giant is equipped with heavy arms in the event that humans turn aggressive, so that it cannot be captured. The giant is, however, somewhat sentient, and likely has the ability to make simple value judgments much like a human being can- that a hunting rifle is not actually a 'threat' to the giant when it is not pointed directly at him. Basically, the aliens that sent him don't particularly want to hurt us, but will if we are 'in the way' of their own resource needs and desire for safety and anonymity in the universal stage.

The second hypothesis I had is much more straightforward. The giant is simply a war machine- his 'passive mode' is a low-power option, or made for when the species who made him must handle him. The bump on his head that he sustained while entering Earth may have rendered him passive by default.

The third I think is the most farfetched- that he is a member of an alien race, perhaps a spacefarer that got caught in the planet's orbit and was pulled to Earth. He suffers amnesia and therefore can be used conveniently for any storytelling reason you want. These aliens have heavy rays and artillery instead of claws and teeth. Perhaps an ancient race of aliens that have advanced technology to the point that they are sentient beings in mecha avatars.

What do you guys think the Giant's true purpose was? Was he sent to Earth to be a passive collector of information? Was he sent to destroy all of us to make the planet habitable for his creators? Is he analien himself? Or do you have your own pet theory about his purpose on our planet?