In the original animated series continuity, the Decepticons owe their warlike
ways to their faction's origin as military hardware robots, created by the
five-faced aliens, the Quintessons, while the Autobots were designed as consumer
goods. Following the rebellion that forced the Quintessons off the planet, the
Decepticons - as they named themselves - lusting for power, began a civil war.
The Autobots could not hope to match the superior firepower and battlefield powers
of the Decepticons, and instead turned to stealth, developing the art of
transformation, modifying their bodies so that they could assume other forms. With
this additional power, the Autobots were able to win the conflict, and a period
of peace began, known as the Golden Age of Cybertron, when energy was plentiful
and the planet shone with a golden hue.

Working in secret, the Decepticons also developed transformation technology, along
with new robot-mode flight powers, and, under the command of one of the first of
this new breed, Megatron, they attacked one of the capital's outer cities, killing
the current Autobot leader. As the knowledge, of this act was not made public,
younger robots continued to idolize these powerful new flying robots - until one
such young robot, Orion Pax, was duped by Megatron into allowing him access to an
energy storage facility. Megatron turned on Pax and fatally injured him, but the
ancient Autobot, Alpha Trion, then rebuilt Pax into the first of a new, battle-hardy
breed of Autobot - now, he was Optimus Prime, leader of the Autobots, who led them
against Megatron and the Decepticons as the civil war erupted again.

After five million years, Cybertron was nearly depleted of all its energy when the
Decepticons received word that the Autobots were planning to search for new energy
resources. Following the Autobot ship, the Ark, in their ship, the Nemesis, the
Decepticons boarded the Ark and engaged the Autobots on their ship. Unfortunately,
the Ark drifted too close to Earth and crashed landed in a volcano. All the occupants
of the Ark went into emergency stasis, while the Decepticons on the Nemesis ejected
to South America. There, they scanned the forms of local insects, becoming the
Insecticons. After 4 million years,the volcano the Ark was wedged in, erupted in
Earth year 1984, restarting its computer, Teletraan I. Sending out Spy Satellites,
Teletraan I created alternative forms out of Earth vehicles for any transformers
caught in its scanning beam (Like F-15 Eagles for Skywarp and a Semi-trailer truck for
Optimus Prime). The Decepticons awakened first but later the Autobots did too, thanks
to Starscream's carelessness.

By the Earth year 2005, however, the Decepticons had succeeded in completely
conquering Cybertron, but the attack by Unicron, coupled with the temporary loss of
Galvatron (a reconstructed Megatron) in that same year shattered their forces,
allowing the Autobots to reclaim their home planet and rout their foes. The
Decepticons fled to the planet Chaar, a world of ash and ruin, where they struggled
to survive until Galvatron returned to them and reorganized them into a fighting
force, battling to take back Cybertron.