Megatron is the titular antagonist of the major comic book series, All Hail Megatron. The comic is known for his extreme change in tone, showing the reader what will happen if the Decepticons' plans of Earth's domination of the Autobot's defeat became a harsh reality.
History
Rise to power
While the Decepticons were occupied fighting the Reapers (a squad of hostile aliens) the Autobots left Earth to deal with the greater threat, being a violent raid orchestrated by the Dead Universe. Exploiting their enemies' absence, Megatron and his troops arrived to Earth, and when the Autobots arrived, they could not find them, as the Decepticons ingeniously escaped their clutches several times for months. Secretly abducting Hunter O'Nion, former Headmaster partner to the Autobot Sunstreaker, Megatron and his soldiers returned to Cybertron, where Megatron had Deluge conduct experiments that spawned a swarm of monstrous Insecticons. The experiments culminated in the creation of Bombshell, who Megatron employed in a series of key tasks in his plan.
The Insecticon obtained several Autobot codes and secrets from hunters mind, completed Shockwave's long-gestating combiner process, granting the Constructicons the ability to combine into Devastator, and created a working space bridge. The Decepticons later executed a battle strategy that led the Autobots to believe they fled Earth. The plan worked, and the Decepticons used this dupe to their advantage, as Devastator stomped the Autobot infantry beneath his foot and Megatron finally beat Optimus Prime by tearing the Matrix of Leadership out of his chest. However, Prime was able to save his captured Autobot peers by destroying a space bridge that led to a colony of hungry Insecticons, but this bold action put the Autobot commander into a comatose. With the Autobots being either missing or dead, Megatron led his squad of loyal Decepticons to storm New York City, causing astronomical damage, killing hundreds of civilians, and taking the huge town over. After only a day of raided major American cities, the United States was firmly in Megatron's control.
Conquest
As the Decepticons began attacking other countries around the globe, Megatron was questioned by Starscream on what the next step in his plan was. Megatron was recalcitrant and obstreperous, so he merely informed him that it was merely time to savor their victory, but Starscream accused him of not having any plans post-victory, and was merely allowing his men to run wild to distract them from any notion of taking power for themselves. What Starscream did not realize was that Megatron did indeed have a plan: to defeat the Autobots, he had created an army of killers and monsters, but in order to create his perfect rule, that army would have to be destroyed, the dissenting, objectionable, and distasteful elements obliterated before Megatron's peace could dawn. Megatron was not distracting his warriors, he was waiting to see which of them would question and turn on him.
Silently sorrowful to already know that such dissent would begin with Starscream, an otherwise-model Decepticon, Megatron withdrew to Israel for some silent reflection amid wholesale devastation. Megatron was hardly shocked to see the Insecticons sided with Starscream, but was surprised and almost overwhelmed when he discovered Devastator joined Starscream's ranks as well. Even still, Megatron remained victorious as he beat both traitors. Yet, Megatron and Starscream were forced to team up yet another time to defend the space bridge from the rebelling humans, and what came to their surprised was that the Autobots charged into battle as well.
Defeat
After assuring Starscream that he would be leader in the future, when his time was done, Megatron confronted Optimus Prime, surprised not so much that his old foe had survived, but that he had bothered to return to Earth. Both leaders had always maintained a policy of acceptable losses through their millennia-long war, so Megatron assumed Prime had come back for selfish reasons, to reclaim the Matrix, but Prime insisted that he had changed, and would no longer allow their cold war to endanger innocent lives on this scale. Megatron scoffed at the notion, reavealing that Prime's supposedly "innocent" humans were planning to nuke New York, killing millions of their own just to get rid of the Decepticons, but Prime retorted that it wasn't just about the humans, but also about the difference between Autobots and Decepticons. The two came to blows, but Megatron triumphed in short order and commanded the Decepticons to depart, leaving the Autobots to be killed by the humans' nuke, but just before they withdrew, he was shot in the face by human soldier Spike Witwicky, wielding a powerful weapon reverse-engineered from Cybertronian technology. Injured and disoriented by the blast, Megatron was finished off when Prime smashed his face in with his own fusion cannon. As he wanted to take leadership rather than just have it fall in his hands, Starscream picked up his damaged leader and ordered the Decepticons to retreat.