The Dark One, or His-Name-Not-Be-Spoken is an evil god who is said to 'predate the realm itself'. It is also said that he is an agent of Chaos, and loyal to Hi- Ahem, Sasha Fierce.
The Dark One was around when it was only one realm, and before Seph. He was loyal to Him and it was said after the realms and universes split, he was still loyal to Sasha. Sasha made Primal's name blotted through History. The Dark One jumped into the other realm. Evil had ruled the realm until recently it was sealed, and too, the Dark One. All of Evil was forced into a realm, a realm inaccessible to anyone. It took a long time, but Sasha escaped the realm, taking some villains and some others with her. Good, in the absence of Evil, created the pg-13 evil. Once the Autobots and Decepticons escaped their dying universes and fled into this one, Sasha decided to create her daughter in the stomach of a human, secretly.
The Dark One is thought to be dead, with Jazzimus Primal being the would-be killer of this Fallen-esque villain.
His lifeless hull (or husk) was seen underground and found by human archaeologists, fossilized. It was now said that he is a Decepticon, judging on his insignia seen minutes after the humans broke the rocks his corpse was a part of. They had then brushed his entire body, putting it in a museum.