The Decepticons provide the yin to the Autobots' yang. Powerful and imperialistic, the Decepticons are considered evil by most Autobots, and indeed many of them enjoy living up to that reputation. The Decepticon are led by Lord Megatron, and are based out of Tarn (polity). Megatron seeks no less than galactic domination, and just about has the power to obtain it.
On ancient Cybertron, the consumer goods robots rose up against the Quintessons in a rebellion that ultimately forced the aliens off the planet. Sentinel Major survived this clash, but he and the rest of his race -— now dubbed "Autobots" -— were robbed of any chance of peace when the military hardware robots, now known as "Decepticons" and led by Megatronus, set their sights on conquering Cybertron for themselves. Two Autobot leaders fell during the war that ensued, and Sentinel Major inherited the Matrix of Leadership and became Sentinel Prime, leader of the Autobots.
Megatronus, however, proved too much for the succession of Primes, and Megatronus and his generals seemed on the brink of conquering Cybertron once and for all. However, during this time Megatronus uncovered evidence of the existence of Unicron, and shifted his focus to preparing the planet for sacrifice to the Dark God. The Decepticon Generals, alarmed at this development, turned against Megatronus, and trapped him in a subspace cell, taking over leadership of the Decepticons themselves.
Under Sentinel Prime's leadership, the Autobots realized that they would never be able to defeat the Decepticons with firepower, and they turned instead to stealth, reconfiguring their bodies to be able to transform into other forms. With the power of his new ability, Sentinel Prime defeated the last early Decepticon leader, and the Autobots won the war, ruling for many centuries. Peace was kept with the use of Guardian robots, sentinels that protected cities, quelled uprisings, and generally did the dirty work of war.
However, the Decepticons eventually learned to transform and also developed a form of anti-gravity that allowed them flight without traditional jet propulsion. Then, one night, deep below Cybertron, a new leader was born: Megatron.
Nine MYBP, the war began anew. Megatron led his army from victory to victory, targeting mainly power centers to fuel his troops and build his forces. While the Guardian robots were powerful enough to strike fear in the Decepticons, even those giant robots were suffering at Megatron's hands. Even the safety of the Autobot Matrix of Leadership was in question, so Alpha Trion (formerly known as A-3) kept it in hiding for many years.
A young, energetic worker at an energy-shipment facility, Orion Pax, was in awe of the Decepticons, but his feelings soon changed when Megatron attacked his workplace and gravely wounded him. The Aerialbots took Orion to Alpha Trion, who was devising new ways to combat the Decepticons. Alpha Trion rebuilt Orion into Optimus Prime, the first of a "new breed" capable of fighting Megatron.
Under the leadership of Optimus Prime, who now possessed the matrix, the Autobots inflicted serious damage on the Decepticon forces, but they were still powerful. War raged across Cybertron, with the balance of power shifting back and forth several times. During this time, the neutral parties in some of the other cities realised that the only way to survive might be to join one or another of the groups. Cities were destroyed because of the war, cities like Tos and Tarn, as both parties grew into larger groups. The main cities, however, Iacon and Polyhex, stood as the capitals of the conflicting groups.
The continued conflict eventually drained Cybertron of its resources, and the war turned from one of conquest to one of survival. Optimus Prime led a team of Autobots on an interplanetary expedition in an attempt to find new resources for Cybertron. That expedition ended when Megatron attacked and boarded their ship. As the Autobots and Decepticons fought, the ship strayed too close to the nearby planet Earth, and it crashed. The Autobots left behind on Cybertron, including the Femmes under Elita One, and the Wreckers under Emirate Xaaron of Iacon, continued to fight the Decepticons of Tos and Varn, led by Shockwave.
For the next four million years, Shockwave commanded the Decepticons, who maintained the upper hand. Groups of Autobot resistance continued to fight, however, from secret bases across Cybertron.
The volcano that the Autobot ship crashed into, Mount St. Hilary, Oregon, erupted during the 1980s, giving off enough heat to power energy sinks onboard the ship, which in turn activated the ship's computer, Teletraan I. Teletraan I immediately sent out a low-altitude satellite to observe the planet the Transformers crashed upon. Teletraan I scanned several native transportation and military vehicles, and used its onboard repair units to reactivate the closest Transformer. This robot was a Decepticon, who managed to keep the repair bots focused on reviving the Decepticons and not the Autobots.
Megatron took his Decepticons and began building another starship. He learned of the people of the planet, but as they were organic life forms, they seemed to pose no threat. Meanwhile, the repair robots managed to eventually reach Optimus Prime and rebuild him, and then the other Autobots. Optimus went out to stop Megatron, and met the humans in the process, rescuing Spike and Sparkplug from an oil rig. These humans were instrumental in teaching the Autobots about Earth. Megatron's starship was shot down into the Pacific Ocean, where Megatron used it for a base for the next several years. He managed to use subspace radio to contact Shockwave on Cybertron, and the two compared technological advances made on Cybertron while the other Transformers were dormant on Earth.
In 2004, the Decepticon army, including Trypticon, marched against the Autobots in Nevada. Metroplex returned fire, but was forced to retreat by the collective firepower of Trypticon and the Decepticon combined robot teams. Optimus Prime was beaten severely by Megatron and Starscream, and the Autobots fled the US. Soon after the decisive defeat of the Autobots by the Decepticons, The President of the United States officially gave over control of the US to the Decepticons. Soon after, around the country the Decepticons began rounding up humans to serve as labor in their energon production facilities.
What If? Worlds
In 1982, Dr. Mindbender discovered an alien craft buried in a dormant volcano in Oregon. Finding an amazing species of giant robot inside, Mindbender removed and repaired them, removing their cores for study and installing controls to pilot them directly or remotely as drones. With powerful mecha at their disposal, Cobra's army seems unstoppable.
The Autobots' desperate attempt to launch the Ark ends in failure, and the majority of Iacon's inhabitants are permanently off-lined. Megatron reigns supreme over Cybertron, as well as many other worlds conquered by the Decepticons, now truly an Empire. The few survivors of the Ark Massacre live beneath the surface of the planet, determined to survive no matter the cost.
After the conclusion of the Second World War, General Robert Savage speaks to the newly formed United Nations, and stresses the importance of not only a world diplomatic force, but a policing force. The General is placed in command of the UN's security forces, which are named G.I. Joes by the people. Joe takeover was gradual, with them slowly gathering up power. Temporary emergency powers somehow become permanent, and keep growing. Under the Joes, peace is maintained and strengthened, and even though there are still seeds of discontent, the Joes faithfully and honorably defend the principles of peace and justice. In 1982, Joe science teams uncovered the Ark and studied it without waking the Autobots and Decepticons inside, using the technology they found to give the United States a huge technological edge. They use this edge to enforce their will across the world.
In the Shattered Glass universe, the Decepticons are heroic, and commanded by Megatron and Cyclonus. They are based out of Polyhex on Cybertron and the Decepticon Interceptor Nemesis on Earth, and seek to prevent the evil Autobots from ruling or destroying both worlds.
The Decepticons expanded their new home, building a Decepticon City near Lookout Mountain. Now Megatron returns to Cybertron, to see what must be done to save their planet.