Optimus Prime is the leader of the Autobots and a father figure to an entire generation of television-raised Generation X-ers.
Beginning life on Cybertron as the naive and pacifistic Orion Pax, Optimus Prime would escape these relatively lame beginnings by learning how to turn into a big damn truck. He used this gift to great effectiveness during the great Decepticon Wars, during which he ran over many, many evil robots. It was also during this time that Prime learned that he HAD THE TOUCH, and that WHEN ALL HELL'S BREAKING LOOSE, HE'D BE RIGHT IN THE EYE OF THE STO-OOORM.
Thanks a lot for getting our childhoods shot to death, Hot Rod.
Following his death in Transformers: the (Good) Movie, Prime went on to be reincarnated in each of the next 9,000 sequel series. Sometimes he got to be a firet truck or a gorilla or a robot gorilla or maybe some kind of fuck-ugly half-mechano-gorilla, but when it comes down to it, he'll always be a big fucking truck to us.
He also agreed to participate in the two recent Transformers films, although the fine print in his contract stipulated that:
1- He had to get ridiculous flame decals like some 9-year old's bike.
2- Shia LeBouf got to crash in his trailer.
Optimus Prime is currently suing Michael Bay and Paramount Pictures for release from his contract, claiming that "Freedom is the right of all sentient beings."