The Cybertron series is sometimes referred to as the final part of the "Unicron Trilogy," due to a set of loose continuity connections with the preceding Armada and Energon shows. In 2006, as the line was drawing to a close, Hasbro released a number of repaints to meet demand. Since it seems like Optimus Prime figures are pretty much always popular, Hasbro dusted off one of Prime's figures from the Armada line, and released it with some minor paint tweaks to join the Cybertron line.
Although "Unicron Trilogy" Optimus Prime is not the same character as Generation One Optimus Prime, almost all Optimus Primes transform into trucks,* so there's little surprise here. The colors of this version of the toy have a little less blue and bit more black than is typical for Primes, but most fans should have no trouble guessing which Transformer character archetype is being used here. Besides being a repaint of a mold that had been created a few years previously, this version, itself, went through a few subtle running changes as part of the Cybertron line. My specimen is one of the later variants, including four symbols (which had been used to represent planets of significance to the Cybertron storyline) on the cab.
Since the unifying theme of (nearly) all Cybertron figures was the existence of a "Cyber Key" accessory that unlocked features, one was provided for this repaint (seen to the left of the cab, above). Since the mold was originally part of the Armada line, in which such features were unlocked via Mini-Cons, this was a fairly simple change. The Cyber Key merely required a small Mini-Con peg to be added, and the desired effect was achieved without needing to make any physical changes to the figure itself. The "feature" unlocked on this toy, however, isn't really anything special. If you move the key (plugged into the robot mode's back) up and down, it causes the torso to twist back and forth slightly, intending to represent the robot punching, but it really doesn't go far enough to make the effect convincing.
Fans of the original version of this mold often affectionately refer to it as "Bendy Prime." It certainly is one of the more highly articulated toys of its era (or since, actually), even without the use of the "punching" feature.
*Ironically enough, one of the exceptions is an ape-form Optimus Prime, which was released a short time after this toy, using a mold created for Beast Wars 10th Anniversary Optimus Primal.