We finally arrived at the final movie to rewatch, Transformers: Dark of the Moon, and we begin with the big bad himself, albeit it’s immediately clear: Sentinel Prime, voiced by Star Trek legend Leonard Nimoy. In the movie he’s the once noble and compassionate ex leader of the Autobots, and Optimus Prime‘s immediate successor, but secretly from everyone he had reached a secret alliance with Megatron to end the Great War by sacrificing another planet… Earth, of course. As soon as he’s reawakened, his betrayal becomes blatant, and the Autobots have to put him down to save their planet of adoption. The original Sentinel is indeed Optimus’ predecessor, but his story is a tad different: let’s see together.
Sentinel’s story began some twelve million years ago on planet Cybertron, at the time the Cybertronians were still slaves of the powerful Quintessons. Sentinel was different from most of his brethren: extremely large, to the point that he dwarfed nearly all other Cybertronians, he had a physical power to match his size, and the Quintessons knew he would have been wasted as a simple slave. In order to better exploit his unique characteristics, the slavers equipped him for battle and 
turned him into a gladiator for their own amusement, forcing him to fight his brothers to the death in front of a cheering crowd. Sentinel faced and defeated a number of adversaries, until he faced none others than Prima, the first Cybertronian ever created by Primus himself: he was no match for one of the Firstforged, and he was swiftly defeated… but Prima refused to kill him, and instead he attacked the Quintessons, with the only result of getting destroyed in Sentinel’s place. This experience deeply impressed Sentinel, and he would have carried within himself the weight of Prima’s death for the rest of his life. Then, finally, part of the Cybertronians rose against the Quintessons in forces, and managed to reclaim Cybertron for their own people. This state of peace, however, didn’t last: the Cybertronians were still divided in castes depending on the function the Quintessons had chosen for them, and they formed groups hostile to each other for the control of the planet. Sentinel wished to live in peace, and thus joined forces with the Autobots, led at the time by Guardian Prime; the Cybertronians who had served in the military, renaming themselves Decepticons, moved war… starting a conflict that would have lasted for eons.
The war immediately claimed a terrifyingly high number of victims, as most of the Autobots lacked the combat experience or the firepower of the Decepticons, who had been fighting their whole existence. Also Guardian Prime was killed in battle, and after him the leadership went to Zeta Prime. Sentinel was among the few capable warriors among the Autobots, and he acted as Zeta’s main advisor and second in command… until Zeta was killed as well, but not before passing the Matrix of Leadership to Sentinel, who became known as Sentinel Prime from there on. As a gladiator, Sentinel Prime had learnt to study the adversary and the battlefield before jumping into action, and thus as 
leader of the Autobots he completely changed war strategy, valuing what his people had rather than trying to match the Decepticons on their own field of expertise. It was clear that the Autobots were weaker and less battle-forged than their enemies, so Sentinel Prime bet everything on stealth: he put some of the best scientists on Cybertron at work, so that they could reconfigure the Cybertronians’ body and make them able to change form, hiding in plain sight. Because of Sentinel’s idea, the Autobots became Transformers, and used their newfound power to ambush the Decepticons, take them by surprise, overpower them in their vehicle forms. Soon, Sentinel Prime faced the Decepticon leader Trannis in a bloody and brutal duel, and his past as a gladiator helped him to defeat and kill his nemesis: the war was won. This moment marked the beginning of the Golden Age of Cybertron, a period of peace that lasted between three and four million years… but then the Decepticons came back, a new generation who had obtained the Transformers’ skills for themselves and guided by an even stronger and crueler leader, Megatron. Sentinel Prime tried to put an end to the war before it began anew, but Megatron was too powerful even for him, and he was defeated… but seeing his death as a possibility, he had already entrusted the Matrix of Leadership to Alpha Quintesson, who would have kept it until a new worthy Autobot leader would have emerged.
Sentinel Prime is a warrior forged by countless battles, wary of conflict and wishing to find a lasting peace for his people, whatever the cost. He is much larger and stronger than most Cybertronians, and he can wield proficiently a number of formidable weapons: while he only had a small shield and a ball and chain as a gladiator, he now wields a full body armor, an electro-disrupter that can generate illusions, a solar energy rifle, heavy artillery and most of all an Energon-charged sword; as one of the first Transformers, he can change into a Cybertronian train, gaining extra speed and durability. A formidable fighting machine, Sentinel Prime is a war hero and one of the central historical figure in Cybertronian culture, a selfless and truthful leader who could inspire admiration in both allies and foes. The Golden Age of Cybertron started and ended with him, and for reasons.
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