The original specification of the Generation 1 Optimus Prime specifies that Optimus Prime consists of three components: the humanoid "Brain Center" (which transforms to the truck cab), the "Combat Deck" (which transforms to the truck trailer) and the "Scout Car", a non-transforming six-wheeled buggy called Roller, which can ride inside the truck trailer. All three components can function independently, but injury to one is felt by the other two. However, in by far the most of the fiction, the humanoid robot actually is Optimus Prime, with the other two components treated as mere accessories that disappear off the scene when Optimus Prime transforms from truck to robot mode.