Optimus Prime is the leader of the Autobots. His backstory may vary depending on the medium. For example: In the Marvel Comics, he was the gladiator in Iacon than then enrolled into the Autobot army when the Decepticons declared war. In the cartoon he was a normal civilian named Orion Pax, that was nearly killed by Megatron and resurrected by Alpha Trion, renaming him "Optimus Prime", with his new body he went on the mission to stop Megatron.