Transformers

Whereas the Earth is the home of a variety of organic-based lifeforms, the planet of Cybertron is the homeworld of a race of robots which have the ability to transform into other mechanisms, with each Transformer having its own unique disguise.

The Transformers are divided into two separate camps: the good and just Autobots, who are led by Optimus Prime (whose disguise is a red 18-wheel semi truck); and the evil Decepticons, who are led by Megatron (who transforms into a gun; there's a good deal of size-shifting involved with Megatron as well). With fuel supplies (called Energon Cubes) on Cybertron running low, both forces travel through space looking for a new source, which leads them to Earth, which from their perspective in rich in the minerals and chemicals they need.

Disguising themselves as cars, airplanes, boats, etc. easily recognizable to humans, the Transformers engage in a secret war for control of Earth's bountiful natural resources...