Megatron is the leader of the Decepticons and the main antagonist in the Transformers live-action film series.
Megatron was one of the main instigaters of the great war on Cybertron. The two sides fought for the All Spark, but it was lost in space. Megatron located it to Earth, but he crash-landed in the Arctic. Captain Archibald Witwicky re-activated Megatron's navigational system. Megatron was taken by Sector 7, a human organization that had also taken the All Spark.
The Decepticons and Starscream attacked Sector Seven and Megatron was able to break free of his icy prison. He meets Starscream who tells him the humans took the All Spark. He tells Starscream he failed him again.
The Decepticons were fighting against the Autobots in Mission City, but the Autobots retreated when Megatron arrived. Jazz tried to stop him but was knocked away and tore in half on top of a building. He saw Optimus, turned into a jet and knocked him through a building and grappled with each other. He threw Optimus away and then blasted him into a building. Megatron then chased after Sam Witwicky, who had the All Spark. He nearly killed Sam by knocking him off a building, but Optimus caught him. Megatron pounced on Optimus and all three crashed onto the street.
Optimus told Sam to shove the All Spark into his chest to destroy it. He and Megatron fought each other, and Megatron was clearly winning. Blackout tried to help Megatron, but he was destroyed by the military. Megatron was then blasted multiple times by the military, injuring him. He tried one last time to take the All Spark, only for Sam to shove it into his chest, killing Megatron and seemingly destroyin the All Spark. His body is disposed of in the ocean.
Revenge of the Fallen
The Constructicons are sent to resurrect Megatron. They jump into the ocean and find Megatron's body. Since his metal body parts have been damaged, the Consructicons turn on Scrapmetal and rip him apart to replace them. A sharp of the All Spark is used to revive Megatron, and he flies off to the Nemesis, where he is confronted by Starscream, who had fled from Mission City. Megatron attacks Starcsream for leaving him and then meets his master, The Fallen. The Fallen tells him the All Spark is in the mind of Sam and sends him, Starscream, and Grindor to retrieve Sam.
After Sam is captured Megatron plans to remove Sam's brain. Before he can do so however, Optimus and Bumblebee attack and Megatron retreats into the forest. Optimus chases him and Megatron catches him by surprise and they brawl. Megatron is not as strong as before because he had his armor replaced by Scrapmetal, who was weak, and he is battered by Optimus. Starscream and Grindor come in and he Megatron gains the upper hand, blasting Optimus away. As he asks Optimus if the survival of his race is worth a single human life, Optimus respons by saying he'll never stop at one and fights all three of them. Starscream's arm is ripped off and Grindor is killed, but the distraction allows Megatron to stab Optimus and kill him. He and Starscream flee.
The Fallen leaves the Nemesis and tells all of Earth to hand Sam to the Decepticons. The Decepticons arrive in Egypt to retrive the Solar Harvester, a device that can harvest energon from the Sun. He realizes that Sam can revive Optimus with the Matrix of Leadership. He tries to stop him but fails and Optimus is brought back to life.
Megatron almost succeeds at killing Sam but he retreats from getting blasted by human gunfire. Jetfire sacrifices himself and gives Optimus his parts, making him more powerul. He destroys the Solar Harvester and fighst The Fallen. Megatron tries to save his master but half his face his blown off and he is blasted through a building. He can only watch as The Fallen is killed, much to his horror. Starscream tells him that sometimes, cowards do survive, and they retreat.