Decepticons (Earth-9107)

"All Hai lMegatron" The Decepticons are one of the primary factions in the Transformers mythos. They are typically concerned with such things as conquering Cybertron, defeating the Autobots, amassing large quantities of energon, developing powerful weaponry, and beating people up. Not necessarily in that order.

Unlike the Autobots, whose leader is a Prime bearing a Matrix, the Decepticons are led by the most powerful of their ranks. This tends to cause some conflict, given how generally every Decepticon thinks that they're the most powerful. Also, the Decepticons are not exactly the most compassionate beings in the universe, but not all fight for greed. More than a few have a sense of honor, while others believe that Cybertron would be better protected by aggressive expansion. Ultimately, the Decepticons desire to protect their homeworld, even if it is at the expense of others. Usually.

Malcontent
750 million years ago, the Decepticons became the descendants of the Destrons, the opressed of the Protectrons. The Destrons were deemed necessary to cull from Cybertron. Following a war, the Decepticons became soldiers and gladiators, while the Autobots became scholars and scientists.

A New War
400 million years ago, the Decepticons rallied together to fight against the Incompetence of Nominal Prime, the Xenophobia of Sentinel Prime, and Imperialism of Zeta Prime. At first their cause was just, but eventually, the leader Megatron corrupted the ideals of his people, forcing a young dataclerk named Optimus Prime to rise up as the final Prime and lead his people in the war. Eventually, the core of Cybertron was taxed by the war to the point it shut down, forcing the two factions to find a new world to live on.

New Battlefield
When the Autobot Ark crashed on Earth, the Decepticons became scattered throughout the galaxy. 400 million years later, in 1984, Autobot signals were detected on a planet called Earth. The Decepticons came like moths to a flame to Earth, reigniting the war in secret, until their public reveal in 2018.