Optimus Prime's History
In the years before the Great War, Orion Pax was a member of the Cybertronian Senate. Although Orion claimed that he merely sought to bring order to a disorganized and chaotic Cybertron, and even maintained a nominal friendship with the miner turned civil rights advocate Megatron, this affable facade concealed his authoritarian ambitions and his insatiable lust for power. Orion recruited other Cybertronians who shared his goals, among them the law clerk Ultra Magnus, whose expertise Orion used to keep his activities legal until the time was right. As a reward for Magnus' service, Orion assigned him command of an enforcer squad that would be "capable of bringing true order to Cybertron". After the squad branded themselves as the "Wreckers", Pax sent them to launch a terrorist attack on the Senate, ordering them to abduct senator Shockwave and subject him to the brain-damaging empurata procedure.
Controlling the Senate was not enough for Orion. To truly succeed in his power grab, however, Orion needed an advantage no one else on Cybertron could hope to match: when Jetfire and Starscream visited the Senate to secure funding for their research on Cybertron's Titans, Orion immediately took an interest in their proposal to excavate and reawaken Metroplex, the Titan they'd partly unearthed near Iacon. Although Jetfire took an interest in the proposal, Starscream, unsure whether they could trust their would-be benefactor turned down the offer. Later that day, Orion pulled some strings to have Megatron released from prison after his latest rally turned violent and ended with his arrest. Orion's demands that Megatron stop his protests sparked a final argument between the pair, which escalated into physical violence and, eventually, Megatron shattering Orion's windshield and declaring that their friendship was over for good.
At some point afterwards, Jetfire, worried about the day when their funding finally ran dry, went behind Starscream's back to take Orion up on his offer. However, Starscream had secretly tailed Jetfire to the meeting with Orion's inner cadre; when Pax overheard the noise, he had Bumblebee and Prowl capture Starscream and bring him before the group. Starscream fled before the Autobot leader could execute him, but as a result Jetfire now permanently stood with the Autobots.
Subsequent events are unclear; some point after this series of events, Orion took on the name "Optimus Prime", overthrew the Senate, and plunged the planet into global war against Megatron's Decepticons. Eventually, he and his followers left Cybertron entirely and travelled to Earth with the intent of plundering its supplies of Rarified Energon. Megatron pursued them off-planet, while other Decepticons arrived later to help defend Earth, and the battles between the two factions grew increasingly destructive. Finally, with the Earth in ruins and on the cusp of an unwinnable battle against their foes, Megatron felt that there was no other way to keep the Decepticons alive other than sacrificing himself and buying time for Starscream to take the remaining Decepticons offworld and into hiding. After a brief battle, Optimus triumphed, beat Megatron to the brink of death, and went on to pillage the Earth before returning to Cybertron.
On the way back to Cybertron, Optimus granted Ratchet permission to use a spare protoform to revive the fallen Bumblebee. Bumblebee returned as the more powerful "Goldbug", but was disappointed to learn that Prime had only sanctioned the procedure because they had material to spare, not out of any kind of affection for his lieutenant. With the Decepticons scattered and on the run, the Autobots set about rebuilding Iacon. However, when Goldbug warned Optimus that Prowl was planning a coup, Optimus arrogantly informed him that he could deal with whatever Goldbug was planning. When Goldbug pushed the issue, Optimus savagely beat the little Autobot as a reminder as to who was in charge. Unsurprisingly, Goldbug fell in with Prowl instead, who sent Goldbug to assassinate Prime on his new throne in Iacon, which he had renamed "Pax" in honour of his former identity. Goldbug fought hard, but was ultimately unable to deliver the killing blow against the much larger Autobot and retreated.
By the present day, Cybertron had balkanized into three distinct, feuding fiefdoms, each ruled by one of the three Autobot warlords. Optimus Prime maintained control of Pax, but the treacherous terrain of the Chrome Ridge prevented him from expanding his territory to the Static Zone which divided his territory from Goldbug's capital of Gold City. The freelance bodyscrapper Blurr occasionally worked for Optimus. After Megatron retook Gold City and deposed Goldbug, Ultra Magnus told his spy Wheeljack that Optimus had plans for Starscream's disembodied spark, which held the secret of how to rouse the Titans from their slumber.