Before time began, there was a vast being called Primus. We know not where he came from, only that he possessed a cube called the AllSpark, which held the power to create worlds and fill them with life. After untold eons of battling with Unicron, the Great Devourer, Primus had to rest, and converted himself into a vast mechanical planet called Cybertron. Fearing Unicron's return, Primus used the AllSpark to create a race of robotic organisms who could fight him off. That is how the Cybertronian race was born.
In the beginning, there were only thirteen. All of them were named Primes, but their true leader was Prima. Primus gave Prima a special and powerful spark container containing a small piece of the AllSpark. This container was known as the Matrix of Leadership. He provided them with a plentiful fuel known as Energon. For a time, the Thirteen lived in harmony...until Megatronus Prime, overseer of entropy (the orderly dissolution of all things in preparation for the next creation), became obsessed with destruction. His obsession led him to the Chaos Bringer-Unicron. Unicron imbued him with great power on the grounds that he serve him forever.
Megatronus agreed.
Megatronus traveled back to Cybertron, and brought with him tiny, germ-like robots containing Angolmois energy, the stuff of Unicron's demonic spark. These germ-like robots eventually evolved into what are known today as Mini-Cons. However, the Angolmois they were coated with infected several reserves of Energon, corrupting it into an evil and potent energy source called Dark Energon. While Unicron's "germs" infested the planet, Megatronus himself attempted to compromise the systems of Primus himself. However, Prima was able to fend him off. Primus took away his name, and wiped it from the memories of all but a few of Cybertron's residents, by now plentiful. Prima and the Cybertron Elite Guard fought Megatronus off the planet and sent him and his new master through a black hole, but in the process, Prima was fatally injured.
Before his death, he passed the Matrix of Leadership to his general, Alphamon. Alphamon took the Matrix and became the second leader of the Cybertronian race, Primon. With Prima's death, his spark joined the Matrix of Leadership. Eventually, Primon's life, too, came to an end, and he was succeeded by another bot named Nova, who took up the Matrix (which by now contained Primon's spark as well) as Prime Nova. It was during Nova's time that Dark Energon was rediscovered by a bot named Violus. Corrupted by the Dark Energon, Violus became the first, and, at that time, only, Decepticon. He began rallying troops to join him. Eventually, the Cybertronians split into Autobots and Decepticons, the Autobots being more numerous. This was the start of the first Great War. Needless to say, this ended rather quickly. The Decepticons inhabited Kaon and its surrounding territories, creating underground battle rings and such to occupy themselves.
Even as separate factions, the Autobots and Decepticons lived in what could be considered harmony, for a time. However, there were a few more clashes with the Autobots eventually, after the Decepticons' numbers increased, but the Autobots were victorious each time. After Prime Nova came Zeta Prime, and after him, Sentinel Prime. Sentinel, however, did not keep the Matrix with him. In fact, the Autobot High Council did not deem him worthy of the Matrix. A mysterious member of the Council known only as A3 took the Matrix and hid it away in the Core of Cybertron with the help of Omega Supreme, the only bot able to access the Core. It was early in Sentinel's reign that a great gladiator who christened himself Megatronus, after the Fallen, rose to power in the fighting rings. As the crowd roared during his latest victory, they began chanting a shortened version of his name. They called him not Megatronus, but simply...
Megatron.
Megatron became the leader of the Decepticons. It was he who strengthened the ranks of the Decepticons, arming them with powerful weapons. He led the Decepticons to attack the Autobots once more. This time, however, the Decepticons, using Dark Energon reserves, were able to hold their own. Megatron, during this siege, brought an end to the life of Sentinel Prime.
A former Hall of Records worker named Optimus, along with a courier named Bumblebee, a medic named Ratchet, a battle-hardened warrior named Ironhide, a historian named Jazz, a cyber ninja named Prowl, a powerhouse named Bulkhead, a femme-bot named Arcee, and a soldier named Cliffjumper, brought the corpse of the freshly dead Sentinel Prime to the Autobot Council, who named Optimus the new leader of the Autobots-Optimus Prime. Prime and his team ventured with a newly reawakened Omega Supreme (who had since been offline, masquerading as a ship called the Ark) to the now Dark Energon-infected Core to retrieve the Matrix of Leadership. The Core, which contained Primus's spark, imbued the Matrix with a piece of his spark to keep him alive while he shut himself down for repairs and gave it to Prime. As Primus shut himself down to prevent further damage, Optimus ordered crowds of Autobots to leave the planet to avoid Dark Energon infection, attacks from Decepticons, and the Cybertronian equivalent of starvation (since the manufacture of weapons as well as the numerous battles had nearly depleted the planet's pure Energon supply). Optimus Prime and his crew attempted to fend off the Decepticons for months, but they, too, had to evacuate in Omega Supreme, who had since returned to stasis. However, Megatron and his troops pursued Optimus and his crew in the Nemesis...