While the precise origin of the Dark is unclear, it is certainly a very powerful, ancient, and dangerous entity. According to the stories The Doctor and his companions heard, it is a sentient evil that is the remains of the void that existed before the Big Bang, dispersed across the universe at the moment of creation but reforming over the aeons around what would become known as the planet Akoshemon.
The influence of the Dark ensured that evil flourished on Akoshemon and the planet’s inhabitants were constantly embroiled in war and atrocities, history stating that the natives committed every atrocity known to exist, until The Dark eventually achieved corporeal form as a single living being. Around 1482 AD, a group of humanoid space travellers arrived on Akoshemon and learned the truth behind the planet’s evil, tracking the malevolent influence that afflicted the planet to its lair and destroying its physical form with fire, subsequently burying the ashes in a crypt on Akoshemon’s moon.
Because the evil of the Dark existed outside of the natural physical laws of the universe, its mind survived, trapped within the ashes, even if it was still somewhat bound by the physical laws of the universe. Knowing that it would need large quantities of blood to reconstitute itself, it used its telepathic abilities to subtly influence the subconscious minds of those in its vicinity, with those who possessed some degree of telepathy being particularly vulnerable to its influence.
Due to The Dark’s presence, when a research team came to Akoshemon to try and create a means of prolonging life, The Dark was able to influence their research to create the Bloodhunter, created from a combination of DNA samples from the planet’s surface being mixed with human DNA and the subsequent creation being force-generated. In appearance, the Bloodhunter’s head consisted of a fleshy stump with a small cluster of eyes and a group of tendrils beneath them, its overall appearance being that of a hairless, short, squat humanoid, with skin the colour of raw meat and a jelly-like substance in place of blood. The project’s goal was to create a life form capable of autonomous self-stasis, but the creature turned out to have increditsible physical strength and an insatiable appetite for blood, which it drained from humans using its tendrils. It proceeded to consume the entire research team when Ravus Oldeman, the Bloodhunter’s creator, released it just to see what it could do, subsequently putting himself in suspended animation to try and escape it.
Around two centuries later, the Bloodhunter was released once again when a mining expedition came to the planet, The Dark also using its psychic powers to redirect the passing TARDIS and force it to materialise as it believed it could use Nyssa and the Doctor as its indirect ‘agents’. Although the miners wanted to claim the planet for themselves, they agreed to help The Doctor investigate the presence of the laboratory, but unintentionally unleashed the Bloodhunter before they could question Oldeman about it. Forced to treat Oldeman with the potentially addictive neurolectrin to allow him to think and communicate, The Doctor and the crew were forced to send a distress signal when they learned about the Bloodhunter, resulting in them being rescued by the Consortium ship Adamantium, commanded by Silas Cadwell, an old flame of the leader of the mining team.
The Bloodhunter was apparently killed by Consortium troops in the initial assault, but its increditsible durability allowed it to recover and attack the team who had been about to conduct the autopsy. Discovering that Cadwell had manipulated events to send the team to that moon, The Doctor initially assumed that he was working to resurrect The Dark based on his personal records, but when they followed Cadwell after he captured Nyssa – whose telepathic powers made her keenly aware of the Bloodhunter and The Dark – he revealed that he had actually been trying to kill it. Cadwell was apparently a descendent of the people who had originally defeated The Dark (It was unspecified if he meant that he was a direct biological descendent or if he had simply inherited the responsibility as part of a cult of some sort), but he had avoided sharing that information earlier as he feared that The Doctor and Nyssa’s vulnerability to The Dark’s influence would have resulted in them convincing others to disregard his planâ and the Doctor had unintentionally proved his point when his actions resulted in the Bloodhunter acquiring the last of the blood needed to restore The Dark when it killed Oldeman after he accompanied The Doctor to The Dark’s grave.
With the Adamantium having crashed as the survivors tried to escape, Cadwell’s only advice was for The Doctor to kill the rest of the crew and then himself to spare them the agony of being killed by The Dark. Refusing to accept that hope was lost eve after realisingthat the Dark had managed to mark him – represented by a dark shadow on his cheek – The Doctor salvaged the remaining neurolectrin, but was uncertain if he was salvaging it because he could use it to accelerate his thoughts and come up with a new plan or because The Dark wanted him to collect it to weaken his will. Before The Doctor could determine the truth, he and the remaining survivors were confronted by The Dark, which had taken on a new form that was the duplicate of The Doctor’s body, chosen so that it could use the TARDIS for itself through The Doctor’s link to his ship.
However, while talking with The Dark, The Doctor realised that, despite its power, it had made a crucial mistake, when it absorbed Oldeman’s blood to complete its return to corporeal form, it had also taken on his current addiction to neurolectrin, and now needed the neurolectrin that it had manipulated The Doctor into acquiring earlier. Convincing The Dark that he would give it the TARDIS and willingly inject himself with the neurolectrin if it spared Nyssa and Tegan – knowing that he had no way to be sure if The Dark would keep the bargain but stuck for alternatives – The Doctor was able to persuade The Dark to restore his ability to act independently so that he could commit one last act on his ownâ at which point he injected the neurolectrin into the Bloodhunter. With The Dark having gained enough of a physical form to be fed on by the Bloodhunter, and with the Bloodhunter now the only source of the neurolectrin The Dark required, the two monsters attacked each other, The Dark killing the Bloodhunter while The Dark was seriously injured. Having gained a physical form, The Dark was now subject to the physical laws of this universe, allowing the last survivor of the mining expedition to break The Dark’s neck before it was set on fire and set back into the abyss that it had been trapped in long ago, destroying it for good.