Sentinel Prime hails from an older time, when Cybertron was the galaxy's crown jewel, and the Transformer race was full of promise and potential. The only known remaining Prime, he personified what a leader should be: wise, compassionate, and a more than worthy warrior. Revered by both Autobot and Decepticon, few would dare stand against his shield and Primax Blade. He is Optimus Prime's direct predecessor, mentor, and father figure.
But when Sentinel was presumably lost forever on board the Ark, Optimus Prime, his hand-picked successor, was left to fill his void. The loss of Sentinel signaled the end of Cybertron's golden age, and the planet spiraled deeper into war. Some who recall Sentinel's reign bitterly remember when Transformers were masters of their fate, rather than scattered to the stars and living as exiles. Above all, Sentinel Prime is a staunch nationalist. He loves his home planet with all of his Spark and will do anything —even go to extremes— to protect it. His intention is to restore Cybertron to its former glory after the war, driven by desperation he turned him against his ideals by siding with the Decepticons.
Upon returning to base, Sentinel betrays the Autobots, kills Ironhide, transports the pillars to Washington D.C. and rendezvous with Megatron. After teleporting hundreds of Decepticons to Earth, he has a confrontation with Optimus, but spares him, in the hope that he would recognize the moral of what he was doing. He demands the exile of the Autobots, who are apparently destroyed while leaving the planet in their space ship. Decepticons around the world began positioning the pillars precisely according to Sentinel's instructions as the first brunt of the Decepticons' assault began in Chicago. Sentinel had chosen a tall, domed building in Chicago's downtown as the focal point of the space bridge. Megatron joined him on the roof of this building, and the Decepticon leader began to gloat about the success of their partnership. Sentinel usurps Megatron and reminded him that Megatron worked for him, not the other way round.
During the final battle, Sentinel battled Optimus, who faked his death, along with all the Autobots. Sentinel proved to be more than a match for the multitude of Autobots and human soldiers. After a prolonged fight, and the removal of one of Optimus's arms, it became obvious that Sentinel was the more powerful of the two. He appeared to have gained the upper hand and was on the verge of executing Optimus when he came under attack by Megatron, who had been goaded into action by Sam's girlfriend Carly Spencer. Megatron had realized how far he had fallen in power within the past few years, and had decided to once again take his rightful place at the top of the command chain. Sentinel was taken by surprise and amassed critical damage. Though this action by Megatron saved Optimus's life, the Autobot leader refused Megatron's offer of a truce and killed Megatron by splitting his head with his energy axe and ripping it off, leaving Optimus and Sentinel alone once more. Finally, Sentinel seemed to understand how far he himself had also fallen, and apologized for betraying the Autobots as he pleaded for mercy. Optimus countered that Sentinel had, more importantly, betrayed himself and his professed ideals, and as his former mentor howled at the ruination of his plans, Optimus unceremoniously executed Sentinel with Megatron's fusion shotgun, avenging Ironhide's death at the same time.
In Transformers: Age of Extinction, his remains are used by KSI to build human-made transformers. A scene in the film features the remains of his head being used alongside Megatron's head and other fallen transformers.
ALTERNATE MODE
Sentinel transformes into a Rosenbauer Panther fire truck. His weapons include a shield, a double-bladed Primax Blade sword that can be folded into one, and a cosmic rust cannon that causes any metal object that it hits to rust into oblivion, as evidenced when he shoots Ironhide once in the chest and twice in the back.
