Sentinel Prime
Born Infinitus on the planet Caelum, the bot who would become Sentinel Prime gave up his original name to become Sentinel Zeta of the Simfur Temple Guard. During the Dire Wraith Conflict, when the Wraiths attacked Caelum, all Sentinels save Zeta were killed trying to repel the invaders. Alone and with only his Primax Blade and shield, Zeta was nonetheless determined to keep the Simfur Temple from falling into enemy hands, and in a grueling hours-long melee, he single-handedly repelled the Dire Wraith force. His unwavering conviction and fortitude made him a hero across the Imperium of Cybertron, and earned him the intrigue of Septimus Prime and the favor of the Matrix of Leadership. Septimus took Zeta under his tutelage, and in the year 100013410 CE , Zeta succeeded Septimus and became Sentinel Prime, the 1,316th Matrix-bearer.
Following the brief recovery period after the end of the Dire Wraith Conflict, Sentinel Prime mostly upheld the then-current status quo of cybertronian society, with no grand agendas or sweeping reforms to speak of. Sentinel was known for his deep compassion for his people, but was often accused of being ignorant to the social conflicts brewing under his reign; such as the animosities rising between the different social castes of the cybertronian populace, and the rise of anti-organic and xenophobic political platforms and fringe groups. Some historians contend that Sentinel was aware of the flaws in old Imperium-era society, but did not do enough to properly address and remedy them in spite of his good intentions
The burgeoning social tensions reached a tipping point at Megatron’s establishment of the Decepticons, who plunged the Imperium of Cybertron head-first into the Great War. Sentinel Prime quickly committed the armed forces to quelling Megatron and his fellow insurgents, but the Decepticons had managed to build themselves into an effective military and political power to match them. Those close to Sentinel said he became morose as he realized war was inevitable, and blamed himself for Megatron’s rise to power and the hatred that fueled it. He withdrew from the public eye and kept to himself in private chambers within the Primal Basilica, only leaving when his council was sought for the ongoing war effort.
Just twenty years into the Great War, Sentinel Prime vanished mere days before the Decepticon Empire’s first assault on Iacon. There is nothing in the historical record to suggest what happened to him: whether he was killed, fled into exile, or befell some other fate- he simply vanished without a trace. It was around this time, also, that the location of the Tomb of the Primes became lost, and the presence of the Matrix of Leadership within its chambers suggests that it had been removed from Sentinel’s person at some point. It is unknown if these events are related to one another.
Since the re-discovery of the Tomb of the Primes and subsequent explorations of its labyrinthine necropolis, it has been determined that Sentinel’s body is not among those of his fellow Matrix-bearers, leaving him as only the second Prime to not be interred in the Hydrax Plateau. This has only added to his mysterious legacy.