Quintesson

The Quintessons are a bizarre and ancient race of mechanoids, whose dark history and shadowy machinations are bound up with the history of the Transformers, and connections with Primus and Unicron. They prefer subtle manipulation, scheming, and advanced technology over brute force, but if those don't work, they can fall back on the legion of deadly Sharkticons and Allicons at their command and a fleet of battle-ready spaceships as well. However, the Quintessons themselves have zero fighting abilities and are absolute cowards if they have nothing to hide behind. For example, they are seen to be powerless against a Sharkticon revolt.

Fiction
In ages long past, a cold and emotionless race of aliens called the Quintessons created two lines of sentient robots on a planet-sized factory known as Cybertron. One was a line of robots designed for domestic duties and labor (known as Autobots), and the other was a line designed for military use (known as Decepticons). The Quintessons were exceptionally cruel to their creations, eventually leading to wide-spread rebellion, a rebellion started by the Autobot A3. Forced to flee the planet, the Quintessons eventually settled on the small, twisted planet of Quintessa, but fostered an undying hatred of all Transformers for millions of years. In 2005, they were shown to capture prisoners for trial and feeding to their army of Sharkticons. The mock trials held by the Quintesson Court seemed to have no purpose at all (except maybe for the Quintessons' amusement), as defendants were still immediately fed to the ravenous Sharkticons even when the Judge determined them to be innocent. However, the Dinobots managed to rescue the pair of Autobots the Quintessons had captured. Worse, Grimlock inspired the Sharkticons to rebel... by stomping his foot on the ground and telling them to do so. One year (or possibly five years, depending on whom you ask) after the defeat of Unicron, the Quintessons reappeared. They first sent a commando team of Sharkticons to abduct various Autobots (as well as Spike Witwicky, though that may have been unintentional). Upon capturing the 'bots, the Quintessons seemed more interested in interrogating their prisoners than feeding them to the Sharkticons. However, they eventually did find the captured Transformers to be guilty of the crime of... being Transformers. (Spike was guilty by association.)

After Rodimus and the Aerialbots mounted a rescue for their captive friends, the Quintessons attempted to kill the would-be rescuers by destroying the entire planet of Quintessa. After this plan failed, the surviving Quintessons made an alliance with the newly revived Galvatron to attack Cybertron (in return for the fictional Decepticon Matrix of Leadership, which they made up because they needed to give him a reason not to kill them).

The Quintessons betrayed Galvatron almost immediately after the battle had been won, toggling a switch which caused all Transformers the galaxy over literally to freeze where they stood. Luckily, Spike stopped the Quintessons before they had much of a chance to do anything. Despite their betrayal (and the fact that they almost killed him), Galvatron remained an ally (despite that he tried to kill them as well).

Later plots by the Quintessons were no less nefarious. A rogue Quintesson scientist abducted three Transformers and a human for behavioral study, a scheme that nearly killed the entire group after they drifted into a black hole. The Killing Jar Later, the Quintessons revived the deceased Optimus Prime in an attempt to lure all the Autobots into a trap and destroy them with a supernova. However, the Quintessons did not count upon Hot Rod forcing Optimus Prime to overcome his programming, nor Optimus Prime's ability to sacrifice himself to save the Autobots. Dark Awakening Later still, the Quintessons attempted to rewrite history by preventing their loss of Cybertron (which nearly resulted in the very fabric of Time being destroyed).

During the Hate Plague crisis, a single Quintesson was rescued from his infected Sharkticons by Sky Lynx, to restore life to the body of Optimus Prime. The Return of Optimus Prime, Part 1 The Quintesson mentioned that his race had gone into hiding in the farthest reaches of the galaxy. The lone Quintesson's help in restoring Optimus Prime and several other Autobots was vital in curing the galaxy of the Hate Plague, but his race was never heard from again.