The Drengin Empire is a ruthless, militaristic species bent on the total conquest of the galaxy. They stand over 9 feet tall, with mouths full of razor-sharp teeth. The Empire fought a civil war in 2226 with its own sub-species, the Korath, where the Drengin were ironically the relatively benevolent party in that power struggle.
The Drengin believe that all non-Drengin species should be enslaved. For thousands of years their primary target had been the Arcean Empire, which they first encountered hundreds of thousands of years ago. Together they invented the stargates, which the Drengin promptly used in a failed attempt to invade the Arcean home world. That aborted attack resulted in a still-burning enmity between the two and the end of any cooperation.
The Drengin are capable warriors. Unfortunately, their maliciousness does not interfere with their cleverness. They are cold and calculating in their cruelty. They have advanced technologies in areas that are, frankly, unspeakable.
The Drengin’s failure to have already conquered and enslaved the entire galaxy is amazing given their ruthlessness, ambition, and brutal efficiency. They had invented death furnaces to incinerate slaves for energy while human beings were still trying to take out the Neanderthals in Western Europe. They had already enslaved the Torians through brutal interstellar invasion via a stargate that had to be auto-piloted across a sea of stars over tens of thousands of years – all while humans were still walking past fields of wild wheat, unaware of the transformative food source, and moving their hunter/gatherer tribes to the next herd.
The only thing that kept the Drengin from the humans' doorstep was the Empire’s lack of convenient interstellar travel. The Drengin invasion of Toria was a one-time thing, an effort that took thousands of generations to accomplish. Even then, it ultimately proved to be not worth the effort. What the Drengin needed was a convenient way to invade and conquer planets. The humans solved that problem with the invention of hyperdrive.
Thanks to hyperdrive, humans could visit this vile species in person (and vice versa) instead of merely trading obscene communications. At the time, Earth thought that the Drengin had moved beyond violence and war like any advanced civilization. A delegation of peace activists was sent to Drengi to negotiate a goodwill treaty in 2176. The humans haven't heard back from them, but it is safe to assume the Drengin thought they were delicious.
After the Dread Lord war of 2225, the Drengin were able to accomplish their greatest ambition – total domination of the galaxy. Their old foes, the Arceans, have been bombed back to the Stone Age. Their former slaves, the Torians, are now harvested as luxury meals for wealthy Drengin elites. The humans have seen all their colonies ravaged, save for Earth, which is protected behind an impenetrable force field. The future looks bright for the Drengin Empire.