Sentinel Prime was the Former Autobot Commander and mentor Optimus Prime, his successor as Autobot leader. He was always patriotic to a fault towards Cybertron, and was a strong willed and determined leader, who held a firm belief in the position of his race in the universe, and demaned respect from all around him, which he earned by proving himself a fierce and powerful warrior, Sentinel was charged with the safety of his secret weapon, the Pillars which he belived could save their dying planet. Eventully, his hopes to revive Cybertron to its golden age glory changed him, and He betrayed the Autobots to secure Cybertrons survival, but was killed by Optimus in a final duel a team the climax of the Battle of Chicago.
Sentinel Prime was a direct descendant of the first Cybertronian, Primus, and was believed to be the last of the Primes. He told tales to his much younger Cybertronian brethren of how the Dynasty of Primes had called upon a legendary artifact, the star-powered AllSpark, to give life to their world. But the AllSpark had been lost to history, and their world had tumbled through the cosmos without a star to orbit for eons. Sentinel Prime had plans to rectify this, and he gathered followers who believed in his path to a new age of life on Cybertron. With the help of Optimus, Megatron, and their legions, they searched the planet for the legendary artifact and a way to power it. However, there were the Thetacons, a tribe of separatist Transformers who disbelieved in Sentinel Prime's vision, and warred against him and his followers. This conflict ended when, with the help of Wheeljack, a sun to orbit was brought to Cybertron, and the AllSpark discovered and energised.
Sentinel was a direct descendant of Primus, the first Cybertronian, and one of the last surviving Primes. With a firm but just hand, he ruled the Autobots before the war.
At some point before the War on Cybertron, Sentinel Prime led a mission to find a new sun for Cybertron. In the final days of the War of Cybertron, Sentinel Prime gave command of the Autobots to his student, Optimus Prime. Around this time, he made a deal with the Decepticons for the future of his home. Sentinel then departed aboard The Ark, hoping to transport his secret weapon, the Pillars , to safety, knowing they were te only hope of saving Cybertron. However, his ship was shot as it left orbit, sending it and its passengers into deep space.
It Eventully crashed on Earths Moon. This was in fact Sentinel's plan all along: to take the Pillars to space and meet up with his new ally Megatron. However, when the Ark crashed, it knocked Sentinel into stasis and killed his entire crew. Megatron later went to Earth, but ended up trapped, frozen in the Artic until he was pulled out by Sector 7.
When Sam Witwicky launched into a rambling lecture on the nature of space and time while in a trance brought on by the knowledge of the AllSpark entering his mind, he recalled Sentinel Prime's "expedition" to find Cybertron a new sun, commenting that it took "fourteen galactic convergences" to get an echo.
After finding the power core of the Ark in Chernobyl, Optimus found out that the Ark was on the moon, and he and the other Autobots went to retirive Sentinel and his Pillars. They found the dormant Prime and took him to Earth, where they kept him at the N.E.S.T. Base. When Sentinel awoke, he angrily attacked Optimus, before realising he was "among friends" . Sentinel asked where the Pillars were, and was told he only saved five, including the most important Control Pillar. Sentinel they scanned an Earth Alt mode and took a drive with Optimus, who offered to return the Matrix of Leadership to him. Sentinel denied it, saying that On Earth, Optimus is his teacher, not the other way around.
Later, as Sentinel was being moved, the Autobots were chased by the Dreads. Altough they killed the attackers and reached the N.E.S.T HQ, Sentinel knew everything he and Megatron planned was now in place. He dropped the Ancient Prime facade and revealed he had turned on the Autobots and made a centuries old alliance with Megatron to Ironhide before shooting the veteran Autobot with Cosmic Rust. Sentinel then tore into N.E.S.T headquaters, ingnoring its staff and killing any in his way. The Autobots Mudflap and Skids tried to fend Sentinel off, but he killed both of them, ransacked the base, and stole back the Pillars.
Sentinel then met up with the Decepticons at the Lincoln Memorial where he began to activate the first step in his master plan: Letting the dormant Decepticons hiding on the moon reach Earth and launch an attack on Chicago. Optimus found and tried to fight Sentinel, but the more experienced Prime defeated him, but Sentinel spared his life. Sentinel then decived the United Nations, telling them that the Deceptcions would take the resources they needed and leave if the "Autobot Rebels" were exiled from Earth. This was a clear lie, but the Autobots were exiled anyway, allowing Starscream to blow up their ship, seemily killing all of them. Believing his only enemies to be dead, Sentintel had the Deceptcions conquer the city and place the pillars in stratigic locations around the world. He then slammed Megatron into a wall, reminding the Decepticon that they were partners, and that Prime was not his servent like Megatron would like to believe.
With the Pillars in place, Sentinel activated the space brigde, and Cybertron emerged in Earths orbit. Earth was not without defenders, however: Optimus and the Autobots had, in fact, staged their deaths, and had arrived in Chicago to stop Sentinel's plot. Optimus shot out the control pillar, deactivating the bridge, leading a furious Sentinel to engage him in battle once more. Unlike their last bout, Optimus held his own, leading Sentinel to call upon Decepticon fighter ships to fire on his ex-apprentice, while he broke off to fight his way through the other Autobots in an attempt to escape. NEST soldiers destroyed the ships, allowing
Optimus to pursue Sentinel and re-engage him, but Sentinel overpowerd Optimus, cutting off one of his arms and beating him to the ground. Sentinel rose his Primax Blade, ready to end Optimus for good, but was shot in the back by Megatron, who had grown paranoid that Sentinel would end up leading the Decepticons and dispose of him afterwards. Megatron beat the already exhausted Sentinel down and punched him around, knocking off Sentinels war helmet in the process, and leaving him wounded on the ground. This gave Optimus the chance to attack Megatron, pulling the Decepticons head off and dumping it on the ground. Optimus then picked up Megatron's Blaster and turned to Sentinel. Sentinel said that he only wanted their race to survive, and that was why he had to betray him. Optimus only said he betrayed himself, before shooting Sentinel In the chest the same way Sentinel had mercilessly executed Ironhide, before firing a second and final blast at Sentinel's head, killing his old trecharous mentor for good, and avenging Ironhide and the others he had killed.
Following his death, Sentinels body was taken and dinsmatled, his head was removed from his body and used for study by KSI. (His head can be seen while Brains was talking about Galvatron)