The Great One

The Great One was a giant, a massive tick-like insectoid alien.

Biology
The Great One's shell was nearly impenetrable. Coupled with how its feeding process could bring the ground to life as an extra defense, it was very difficult to attack the Great One.

History
The Great One traveled from world to world, sucking the energy from the planets it landed on to feed itself. This process poisoned the worlds it visited to the point where they would implode. On top of that, it was followed by a group of worshipers (a leader, an interpreter, and an enforcer) that wanted to make sure that it would complete its task.

The Great One was responsible for the complete destruction of the planet Arburia about a week before it tried to destroy Earth. It was eventually destroyed from the inside by Ben Tennyson as an Arburian Pelarota named Cannonbolt. This was a somewhat ironic accomplishment, considering the Great One was killed at the hands of a surviving member of the last species it tried to kill off.