Many works of Transformers fiction revolve around two alien robot factions with the power to transform. These two factions hail from the planet Cybertron: the heroic Autobots, led by Optimus Prime, and the evil Decepticons, led by Megatron. Some interpretations of the lore replace them with their direct descendants, the Maximals and Predacons. Another villainous faction, the Terrorcons, may also serve as a stand-in for the Decepticons. These factions may be present at the same time as their Autobot and Decepticon counterparts. Both factions are at war for energon, an energy source that can power themselves and their planet. When their home planet Cybertron is rendered uninhabitable as a result of the war, both factions attempt to escape their homeworld in an attempt to find more energon. It is after this that they find their way to Earth; they may either crash-land into prehistoric Earth on their respective ships and lay dormant until the modern day, escape to Earth from Cybertron, or live amongst humans. While on Earth, they assume the appropriate vehicle, device, or beast forms and continue their war. The Transformers are oftentimes aided by human allies like Spike Witwicky and Mikaela Banes who are roped into their conflict; humans play a major role in Transformers: EarthSpark, which significantly changes the origin of new Transformers by introducing Terrans, Earth-born Transformers who are emotionally bonded to humans through special wearable cyber-sleeves.
