Optimus Prime has restored peace but paid a terrible price. He has lost all memory of ever being a Prime and reverted to his pre-Prime state, Orion Pax, rekindling his friendship with Megatron and the Decepticon leader seeks to use this new turn of events to his advantage. Desperate to rescue their leader, the Autobots launch an audacious plan to save 'Orion' which leads them back to Cybertron.
Transformers: Prime (Season 2, Volume 1) - Orion Pax
The Autobots Rally To Save Their Leader