The Cybertronians are the true name of the "species" that humans call "the Transformers". Cybertron is their homeworld, an artificial planetoid orbiting a distant star. All many factions of Transformers are Cybertronians, the Autobots, the Decepticons, the Maximals, the Predacons, even the Vehicons. Not all Cybertronians can transformers, the "art" of transformation was not developed until the Second Cybertronian Civil War, the first war fought between the Autobots and the Decepticons. However, since that time, all Cybtertronians can transform, only those predating the Second War may not have this ability.
Cybertronians are a machine race, they do not breath or consume food or drink water like biological races. Instead, Cybertronians fuel on a rare substance call Energon. Its in raw form it is actually harmful to them (although not to organic life) but in its processed form, it is essential to their survival. Cybertronian technology has developed to the point where they can convert most forms of energy into Energon.
All Cybertronians carry a "spark" inside them, as long as this spark endures, the Cybertronian can be rebuilt, no matter how much damage the unit has sustained. If it is extinguished, the Cybertronian dies for good. It is a common belief amongst the Maximals that their sparks are a part of or a fragment of Primus, the mythical creator of the Cybteronian race.
In the so-called Generation 2 comic books, "Cybertronian" was a name a faction of Decepticon descendants took to calling themselves in order to distinguish themselves from the other Decepticons and the Autobots. They're sometimes more correctly referred to as Second Generation Decepticons or some variation thereon.
- These Cybertronians were a result of Decepticon rediscovery of Bio-Morphic Reproduction ("budding") ~4 million years ago on Cybertron. The Decepticons were able to rapidly expand their population using this method.
These new Decepticons left Cybertron in the hands of petty warlords unfit for the future empire and took to the stars to conquer other worlds.
In the modern era, the Cybertronian Empire has adopted an aggressively expansionist stance. They claim to have advanced their society beyond the need for war, but hold little regard for non-Cybertronian lifeforms. Under the cause of improving the quality of life for their citizens, they have conquered many worlds, enslaving or exterminating the native population and cyberforming the planets to create "little Cybertrons."
This was apparently under the direction of the Decepticon progenitor known as the Liege Maximo, who rules them from the planet-spanning structure known as the Hub, which harnesses the networked power of the cyberformed planets. The construction of this network was later revealed to be part of a gambit by the Liege Maximo to ascend to the plane of the Dark Gods.