A silly idea: Megatron, but it's actually just a big suit of armour, like Ultra Magnus. The original one, the miner, is long dead. There was the gladiator, who had survived for the longest. But not even he was invincible.
Shockwave and Soundwave are aware of this scheme because they implemented it. Shockwave is responsible for the technical stuff, while Soundwave evaluates the candidates (reads their minds). Starscream doesn't know and he has actually killed Megatron several times, but Shockwave and Soundwave got a new one before any lasting damage was done.
Except that one time when Frenzy and Rumble found the Megatron. Autobots still remember that day with fear as it was the only time the Decepticons were two blaster shots away from victory. Shockwave and Sounwave call it The Incident.
Starscream is perpetually uncertain. Especially after that one time Megatron nearly dismantled him for the usual traitorous scheme just to be all supportive when he returned from the medbay after nearly being blasted to pieces by a missile. Are those mood swings caused by physical trauma?
slightly angst route for Optimus: You lose hope for redemption of your old friend each time you clash on the battlefield, but the thing is, your old friend is long gone. You killed him and you don't even know about it.
