For those who want a quick refresher on what happened in the Marvel Transformers comic, here is a copy of some of the text from Wikipedia on Optimus Prime's life in the Marvel comics:
In Marvel Comics' comic series, before the Great War broke out on Cybertron, the robot who would be Optimus Prime (before he received the Matrix of Leadership from Sentinel Prime, his name was Optronix) was a Transformer of note, displaying his skills in the Infraformers Sharpshooting Competition. Subsequently, when the war began, Prime quickly made a name for himself as a combat leader. On a mission with the Triggerbots to stop Megatron from claiming the Underbase, Prime was forced to jettison the massive databank into space to prevent anyone from acquiring its power, but with this action, he proved his wisdom and skill to the Autobot Council of Elders; this led to even more rapid advancement, eventually leading him to field command over the Autobot armies.
Four million years ago, Cybertron - shaken from its orbit and drifting through space - came under threat when it floated into the path of a massive asteroid swarm that could potentially devastate the planet. Prime led a group of elite Autobot warriors on the Autobot starship, the Ark, on a mission to destroy the asteroids, and although successful, in the aftermath of this mission the Ark was attacked by Decepticons, hoping to overcome their weakened foes. Intent on keeping the secrets of the Ark from the Decepticons, Prime set the craft on a suicide course, crashing it into the prehistoric planet Earth.
In 1984 A.D., a volcanic eruption re-activated the Ark, which in turn brought the Transformers back on-line. Prime led the Autobots in their opening battles to prevent the Decepticons from plundering Earth's resources, but following their initial victory, the Autobots were all deactivated by Shockwave. Prime was decapitated by Shockwave, and had the energy of the Creation Matrix leeched from his mind to give life to Shockwave's creations, the Constructicons (although Shockwave was unaware that the Matrix was not merely a program in Prime's mind, but a physical object in his chest). Before Shockwave could give life to his next Decepticon, Jetfire, Prime transferred the Matrix energy into the mind of Buster Witwicky, who used the energy to turn Jetfire on Shockwave, allowing Prime to reclaim his body and retake leadership of the Autobots, giving Jetfire true life as a reward.
After a period of effective leadership which saw the activation of several new Autobots including the Aerialbots, who Prime infused with life using the Matrix, Prime engaged Megatron in a video game duel for possession of a super fuel. Prime was victorious, but Megatron implemented a cheat code, allowing him to re-enter the game. Prime was able to defeat him yet again, but in doing so, he also destroyed several of the game sprites, and refused to accept his victory, as he had performed an action that compromised his beliefs about the preservation of life, which he would never have done, had the duel been real. In accordance with the rules of the game, Prime's body exploded and he died. Autobot surgeon Ratchet's subsequent efforts to restore him were unsuccessful, and his body was launched into space, the Autobots unaware of the presence of the physical Matrix object within the corpse. The funeral barge eventually crashed on a giant moon; as it lay there for an untold time, the Matrix reached out to nearby living organisms, studying and recreating them. One such recreated being became known as Death Bringer.
Prime's personality had been copied onto a floppy disk by the technician running the game, Ethan Zachary, who employed him in various video game scenarios he developed. Prime's damaged mind led him to believe that he himself was a video game character, and in an attempt to bring him back to life, Goldbug, Joyride, Slapdash and Getaway took the disk to the planet Nebulos. They built a new body for Optimus Prime, and even upgraded it with the ability to combine with the trailer to form a larger robot. In an effort to keep Transformers off their planet, however, the Nebulans had poisoned their fuel, and the sensation of dying convinced Prime that he was truly alive, and not a game character. To save his life, the Nebulan scientist Hi-Q bonded with him, creating Powermaster Optimus Prime.
Optimus Prime's first actions as leader were to ally the Autobots with Scorponok's Decepticons in defeating Starscream when the later gained the power of the Underbase. When Starscream gained cosmic power from a brief exposure to the Underbase, it was Optimus Prime's idea to let Starscream absorb so much power from the Underbase that it destroyed him. However, the casualties were immense, with most of the Autobots who had come to Earth with Prime being deactivated. His guilt over this was only heightened when his friend Ratchet sacrificed himself to stop a returned Megatron from escaping once again.
With the subsequent threat of Unicron looming, priorities quickly changed and Prime began a quest to locate his old body and the physical Matrix object within it. After losing the Matrix to Thunderwing Prime began to make a series of questionable decisions, including ordering the separation of the recovered Ratchet/Megatron hybrid monstrosity, even though it would mean that Megatron would be saved as well. Shortly after this Prime would surrender to Scorponok in a bid to convince him of the threat of Unicron, an action that dented his troops faith in him. When the Transformers were all transported to Cybertron by Primus to battle Unicron, Prime managed to successfully reacquire and purify the Matrix after Unicron killed Thunderwing and his taint upon it. Prime then sacrificed his life one more time to destroy Unicron by plunging the Matrix into his maw. However, the Powermaster process had been working to fully bond Prime and Hi-Q, and with Prime now destroyed, the process completed itself in Hi-Q's body, and the two minds and souls became one. Hi-Q's biomechanical body was stripped down and reconstructed by the Last Autobot, resurrecting Optimus Prime once more with the two minds now one. Prime joined with the other Autobots on the planet Klo and routed Bludgeon's Decepticons
