From Transformers#1: Circling the star Alpha Centauri, ages ago, was a planet unlike any other in the heavens -- Cybertron. No rock or soil or sand contributed to its bizarre geography. Its content was entirely -- mechanical. Cybertron existed, from metallic surface to core, as a vast Saturn-sized machine world... a world whose origins were lost in the dead past. Yet life had evolved here. It had grown and adapted and thrived in its environment remarkably well. And cities rose across a broad mechanical expanse... cities that were the products of Cybertron's dominant life-form -- the Autobots. Whereas life elsewhere in the cosmos usually evolved through carbon-bonding, here it was the interaction of naturally occurring gears, levers, and pulleys that miraculously brought forth sentient beings. They created a mechanical paradise... a machine-filled landscape where each Autobot went about his pursuits in peace and prosperity. But every paradise has its serpent... and on this world it was Megatron, commander of those who called themselves -- the Decepticons.
In the weeks that followed, Decepticons from everwhere reported for clandestine meetings to learn the logistics of the coming clash, and their parts in the struggle. The wonders of their techology bestowed upon the Decepticons the awesome ability to transform into weapons of unprecedented power. With these tasks completed, all was in readiness for the first assault...
The war spread until it was a global conflict; the forces unleashed were staggering, inconceivable. And each attack upon an Autobot stronghold was orchestrated with the precision of which only finely tuned machinery is capable. As the powers at play grew in strength, Cyberton itself was shaken losse from its orbit -- and sent hurtling through space. And still the war raged across the battle-scarred surface of the runaway planet. Though taken by surprise, and destroyed by the billions in the initial assaults, the surviving Autobots were not defenseless. Each was gifted with the ability to alter his configuration into strange, unearthly vehicles... vehicles of great offensive potential. And while the Decepticons in their armored aircraft shapes swooped down upon the many Autobot city-states erected during the war... the Autobot warriors stood firm and fought back. In time, the magnificent armies on each side of the struggle became known as -- the Transformers.
From Primus, in Transformers#74: Every planet, whole galaxies, even the stuff of space itself -- gone, destroyed... consumed! Leaving only -- the void! Cocooned in absolute nothingness, the force that you now knnow as Unicron slumbered, its terible hunger and lust for destruction finally appeased! But Unicron had not been thorough, and tiny cosmic fragments of the old realms that had escaped the purge reacted with each other. The resultant explosion triggered a chain reaction that led -- over countless trillions of your years -- to the creation of the universe as you know it today! Its sentient core, alert now to the threat posed by Unicron, created a guardian, a Yin to Unicron's Yang. It called its child Primus!
Unicron awoke to find new life teeming around him once more. He did not question why -- he simply began to destroy it over again. Destoyer and Guardian met in a conflict so mighty, the very life Primus sought to protect was being wiped out! The savage irony of this was not lost on either combatant! Primus realized his only chance was to trick Unicron and -- at the cost of his own freedom -- managed to imprison their life essences in barren metal asteroids!
Eons passed, until finally Unicron discovered he could psionically shape his metal prison. Able to transform between robot and planet, Unicron continued his orgy of destruction! Primus, aware of Unicron's escape through the mental link they shared, also shaped his prison... into the planet on which you now stand... Cybertron! He populated it with beings designed to mimic Unicron's transformation abilitites, arming them with a genetic matrix formed with his own life essence! They are the last line of defense against Unicron -- they are you. They are [the] Transformers.
And finally, from Optimus in Transformers Generation 2#12: This is the story of the Transformers. The true story!
Shorn of its mystical trappings, it is a tale of evolution: One being, Primus, becoming a race that could reconfigure their forms into machinery, vehicles, and weaponry. Cosmic guardians whose prime concern was the continued welfare of other races. But as we grew in number, replicating through a process similar to cell division, so the essential purity of our creator's vision was distilled... until finally, in many new Transformers, it simply no longer existed! Chaos ruled. Civil war theatened to destroy all that we had striven so hard to achieve! At this point, some pre-encoded gene kicked into life in all Transformers, initating a race-wide memory loss that was intended to end any further growth.
It didn't last!
While we lay deactivated on Earth, a second generation arose. The process began again, spawning successive generations and, as a by-product... a strange relation! [Ed: the "by-product" refers to the Swarm.]