Sentinel Prime is the main antagonist of Transformers: Dark of the Moon. His transformation is a fire engine. Sentinel was the Prime before Optimus and was the proud leader of the Autobots, until he betrayed them so he could save Cybertron. He was going to create a space bridge and transport Cybertron to Earth and use human kind as slaves, and workers. But he was double crossed by Megatron who shot him in the back whislt he had the upperhand. Slowly Optimus got up and despite Sentinel begging for his life, he cuts of Sentinel's head, letting sparks fly.