Guardian robot

Originating as the Quintessons' Dark Guardian robots, the Guardian robots of the Golden Age of Cybertron were powerful giant blue robots that kept the peace. They gave the Decepticons much trouble during the early days of the war but were eventually overcome.

Only one, Omega Supreme, the Guardian robot of the Crystal City, was ever named, had a distinct color scheme, and was shown to be sentient or able to transform, but it was not revealed if he was indeed unique amongst them in those regards.



Cartoon canon
At the end of Cybertron's Golden Age, the Guardian robots fought against the newly assembled Decepticon army extensively and destroyed quite a few drone warriors. They gave Skywarp the creeps with Thundercracker stating that they gave them a "pounding" in the old days. Shortly before Megatron's first confrontation with the newly activated Optimus Prime, a Guardian's head was destroyed by Decepticon laser fire, deactivating it.

Millions of years later, after escaping an Autobot attack on their time machine facility, the Decepticons found the remains of the damaged Guardian robot. Shockwave managed to reassemble the giant, though he noted that the lack of a head would limit its maneuverability, to which Megatron commented that "A warrior doesn't need a head, just a good strong body."

This Guardian was unleashed upon Optimus Prime and the Autobots until the Aerialbots arrived from the past and merged into Superion. The sheer strength of the Guardian overwhelmed Superion at first, but he retaliated to such an extent that the Guardian was thrown into the air before crashing back into the ground where its body was destroyed.