Peacekeeper

The Peacekeeper is a robot powered by the mysterious "Red Core Energy" built by President Stone. It also has "Prototype Adaptive Technology" that allows it to take in other things and objects. Originally built to help Stone get re-elected (reason unknown), due to his core he started destorying Metro City, and Astro had to shut it down.

Movie
When the Peacekeeper was complete, the science institution was going to place in the blue core, containing positive energy. But Stone, who wanted it to be a war machine, made it grab the red core. The Peacekeeper then went on a rampage and the scientists locked it in a force field and knocked itself out when it tried to use its firepower to get out.

Later, when Astro fled from Stone, the mad president activated the Peacekeeper with the red core again, despite having seen the previous results. The Peacekeeper aborbed President Stone and upgraded itself with other machines into a colossal mechanical monster with Stone's mind. It then went to the surface world to get Astro. Peacekeeper Stone wasn't able to absorb Astro, because he has the blue core. Astro plunged into the robot and overloaded and destroyed it. President Stone survived but was arrested.

Trivia
For comic relief, there is shown to be a toilet on its back.