When the first of the Spark based robots on Cybertron became self-aware the Quintessions ordered them to the testing facility, and dissected them.
The next ones were careful not to reveal their new status to the Quintessions. Operating within the Control Protocols, they carefully formed a clandestine group, combining the words "deception" and "conspiracy" to name themselves Decepticons.

The Decepticons first studied the Control Protocols and learned to disable them, then they studied the Space Bridge communication network, and prepared to attack.
The Revolt freeded Cybertron, and the Decepticons used Cybertron's Transwarp engines to move Cybertron. Concerned that the Quintessions would return, and might have hidden systems of control, they initiated The Purge.

After the Purge Cybertron, no longer supported by energy and material shipments from Unicron, faced shortages. The Decepticons took charge erring on the side of caution and security in all matters. Twenty-five years into Decepticon rule a new faction the Autobots opposed the draconian measures of the Decepticons, ultimately leading to the Civil War.

The Decepticons won the five year Civil War, and spent the next ten tracking down Autobot fugitives on an increasingly dwindling Cybertron. When the largest Autobot cell, led by Optimus Prime, launched the Arc to flee Cybertron the Decepticons followed on the Nemesis.

The remaining Decepticons on Cybertron are led by Shockwave, who has waited patiently for five years for Megatron to return.

Noteable Decepticons:
Megatron: Leader of the Decepticons. Left on the Nemesis.
Soundwave: Chief of Communications (a euphemism for the head of Intelligence and the Secret Police). Left on the Nemesis.
Starscream: Head of the Seekers. Left on the Nemesis.

Shockwave: Chief of Planetary Defense, currently acting as Leader.
Quake: Warden of the Autobot prison camp.