When Optimus Prime transforms from vehicle mode to robot mode, he splits into three components:
- A sentient humanoid robot module, called the Brain Center.
- A wheeled drone module known as Roller.
- A Combat Deck.
It is the humanoid robot module, or Brain Center, that houses Optimus Prime's higher functions, personality, and spark. It is the Brain Center that controls the other two modules by remote.
Prime's original character description as seen in the Transformers Universe comic and the series bible, named the Brain Center "Optimus" and the drone module "Prime", noting that the Prime module is also known as Roller.
When Optimus Prime was rebuilt for the first time into a Powermaster, his three component aspect was not retained in his new body.
In actual practice, however, the humanoid robot was always known as "Optimus Prime", with "Prime" being the most common nickname. The Brain Center is treated like it is Optimus Prime, with the other two modules disappearing from the scene as Optimus Prime transforms from vehicle mode and the humanoid robot going about the business of being Autobot Commander.