Sentinel Prime

Sentinel Prime is a rogue Autobot in 'Transformers: Dark of the Moon. '

He is Optimus Prime's mentor and teacher. During the war that destroyed Cybertron, Sentinel made a deal with Megatron in order to save the planet. They made a plan to rebuild Cybertron on Earth. Sentinel Prime's ship accidently crashed on Earth, however, and he went into a coma. Decades later, the ship was discovered by humans. Optimus Prime came and recovered him and, using the Matrix of Leadership, revived him. It was decided Sentinel have the Matrix of Leadership, but Sentinel said thats ince he knew nothing of Earth he should have it and that Optimus was now his teacher.

Decepticons known as the Dreads chased after Sentinel but was killed by Ironhide and Bumblebee. It was then Sentinel revealed he had been working with Megatron the whole time and then shot Ironhide with the cosmic rust cannon, killing him, before wiping out NEST.

Sentinel, with Megatron and Starscream's help, were able to activate a space gate that allowed Decepticons to get to Earth. Sentinel spared Optimus because he was once his apprentice. The Decepticons took over Chicago and killed most of the people there. However he attacked Megatron during the invasion and took over as leader, leaving Megatron sulking in an area at Chicago.

The Decepticons planned to activate hundreds of pillars around the world and transport Cybertron into Earth's atmosphere. Optimus deactivated one of the pillars as Sentinel needed all of them to re-create Cybertron. Sentinel jumps down the building and fights Optimus and the Autobots while ordering any surviving Decepticons to re-create the pillars. When he was shot down by a rocket-launcher he retreated. Optimus chased him and battled him again. Sentinel ripped off one of one of Optimus' arms and stabbed him in the shoulder. He raised his sword to kill Optimus when Megatron intervened. Megatron had been convinced by Sam's girlfriend Carly that if he didn't kill Sentinel he would end up serving him. He shot Sentinel with his gun and proceeded to attack him viciously and leaved him badly injured. However, Optimus killed Megatron and took the his gun. Sentinel pleaded that all he wanted was the survival of his race and to understand why he betrayed him, but Optimus claimed he betrayed himself and shot Sentinel with the gun twice, killing him.