Many eons ago, thousands of light-years away, on the planet Cybertron, there was a proud civilization of large mechanical beings called Transformers. They lived together in peace and prosperity until a malevolent gladiator named Megatron rose up in rebellion against the rest of the world. He and his followers, the Decepticons, laid waste to any and all who defied their order. Their power and might were overwhelming, and they were quickly able to overthrow Cybertron's rulers, the almighty Primes.
But in his haste to rule over the planet, he accidently inspired a lowly Transformer to rise up and put an end to Megatron's tyrannical reign. His name was Optimus Prime. Optimus and his allies, the Autobots, rose up and battled against the Decepticons. Their power equaled the others, and the ensuing war between Autobots and Decepticons lasted for many eons until the planet was nearly destroyed and their now rare life source called Energon was beginning to run out.
This put both sides at a disadvantage, for the two sides needed Energon to survive. They all abandoned the war and set out across the universe to find more Energon. Their travels landed them on Earth, a primitive planet inhabited by carbon-based life forms called humans. But the Decepticons did not see this planet for it's life. Instead, they saw it as another planet to rule over, and thus, their great war continued on Earth.
The human armies quickly saw that the Autobots were trying to protect them, and the two powers made peace with each other. They fought against the Decepticons, all sides suffering many casualties, and when hope seemed like a distant memory, a new army emerged, seemingly from nowhere, called the Zetas.
Their power was incredible, not unlike the Primes that fell so long ago. The Zetas quickly defeated the Decepticons, and they ordered that all sides make peace with each other. The Decepticons begrudgingly obliged, and, together, they ushered in a new era of peace. They worked together to create many feats of technical engineering previously thought impossible, including a machine that could change their size and appearance to that of a human or a Transformer.
It seemed that the war was finally over. That is, until a Zeta named Zanoid began killing his brethren, forcing the army's leader, Slasher and his wife, Arcee, to use their newly developed technology and hide as humans, and they disappeared without a trace. But Zanoid was the most intelligent of the Zetas, and he was easily able to track them down and slaughter them. But, for as intelligent as Zanoid was, he was never able to account for one thing.
That thing...
Was babies.
Slasher and Arcee created two more Zetas and put them in Optimus Prime's care before they were slaughtered. He took the Zeta children into a large, dense forest and vowed to care for them until they were powerful enough to destroy Zanoid.
And there they stayed for the later end of 18 years...