Azoth did not directly oppose The Doctor during their confrontation, he was nevertheless responsible for creating the primary threat that The Doctor had to deal with during their encounter; with the others mainly victims of Azoth’s experiments rather than making a conscious decision to commit their crimes themselves, it is therefore practical to consider Azoth the villain rather than them.
An artificial life-form, Azoth was created on the distant planet Benelisa, a planet surrounded by various spatiotemporal anomalies such as black holes and white holes, rendering the world a dimensional hot-spot. Their technology was based around organic computers and crystallography – similar to the Zygons, albeit more advanced , to the point that they could encode computer programs into the brains of other living species. Tragically, Benelisa was destroyed millennia in the distant past when a pan-dimensional race – their name for themselves is unknown, when the Benelisians referring to them as ‘the Beast’ – came to the planet and began to feed on the population, draining Benelisa of life. Before their demise, the Benelisians sent out various androids to track the Beast across the universe and eliminate it on other worlds.
Azoth sent out on this mission, built with various self-repair and back-up systems, as well as encoded with instructions on creating a program to eliminate the Beast (Presumably adaptable based on the species he encountered). The program in question was delivered via leech-like, programmed biosynthetic organisms, which transmitted retroviral RNA into the host DNA, rewriting their DNA, causing guanine and cytosine to bind with a non-nitrogenous base. Arriving on Earth in 1822 – it was unclear if he had visited other worlds or if he simply drifted until arriving here , Azoth selected various identical twins as subjects – one twin being ‘treated’ with the program while the other was kept to provide a template sample without Azoth being required to create one himself , Azoth froze one twin in cryogenic suspension while releasing the other back into the world after infecting it with the program, allowing them to pass on the program to their children and continue his work.
Unfortunately, it also rewrote neural pathways in the host brain, with its ‘corruption’ over the following generations since Azoth created it resulting in the descendants of his subjects apparently suffering from schizophrenia, rarely achieving a formatting that would allow the ‘hosts’ to interface with the Beast. Azoth may have been able to correct this flaw if given time, but when one of his subjects attempted to resist his attempts to freeze them, the resulting struggle caused an explosion that damaged Azoth’s equipment and Azoth himself, sending Azoth offline. He was reactivated in 1963 when various descendants of his original subjects were brought together in proximity to his location by Doctor Charles Roley, whose five patients – Captain Dafyyd Watson, Lucy Russell, Peter Taylor, Austen, and Muriel Kreiner (Roley employing Muriel’s son Fitz to work in a garden centre in his manor’s outskirts to help fund his research) – all shared the same hallucination of a mysterious cave. Unable to recall what his mission had been – his systems having worn down through sheer age , Azoth released Neville Tarr, one of his previously-collected subjects, to try and learn what his mission had been, keeping Tarr active to help him even after Tarr was revealed to know nothing.
When the Eighth Doctor and Samantha Jones arrived in 1963 close to Roley’s estate, The Doctor was able to convince Roley to allow him to examine the patients, quickly recognising their shared description of the cave – which Roley believed reflected his patients accessing into a common human archetype that would allow them to tap the positive side-effects of madness – even if he couldn’t immediately remember where he had seen it. While Sam and Fitz Kreiner went out for a night on the town, they were attacked by Azoth and Tarr, but Fitz was able to trick them into thinking that others were approaching before Azoth could do anything more than scan Sam’s mind.
While studying Roley’s notes, The Doctor discovered reference to the leeches – Roley considering them irrelevant growths as they didn’t fit his theories , subsequently analysing one that Roley had extracted from Austen by linking it to a computer program based on the human brain. When the other patients killed Austen trying to put the leech back in – apparently provoked by Roley’s latest experiment causing Watson to regress back to the genetic memories of his own great-great-grandfather, whose twin had been taken by Azoth , The Doctor being subsequently too occupied studying the leech’s effect on the program he’d developed in Roley’s sealed lab to be aware of Azoth’s arrival at the house and his subsequent abduction of Sam and Austen’s body.
Attempting to continue his experiments after analysing Austen to determine the flaws in the program, Azoth ‘infected’ Sam with the program – apparently aware of her unusual biodata due to the machinations of Faction Paradox (“Alien Bodies” and “Unnatural History”) and hoping that her physiology would thus be more receptive to the program , but whether through a glitch in Azoth’s programming due to the previously-sustained damage causing him to make a mistake or Sam’s strange biodata, the program didn’t work properly, ‘shifting’ Sam’s vision so that she could see the Beast but otherwise unable to interface with them, as well as causing increasingly greater damage. Although The Doctor was able to find Sam, he now had two problems to deal with; not only had Azoth now remembered his mission – prompting him to kill the now-irrelevant Tarr , but Watson had begun to explore the mental powers that the leech had provided him with – their cross-circuitry of the subjects’ mind amplified by Roley’s attempts at therapy , and was already leading the other patients in preparing to attack the world that had done so much harm to them in the name of a ‘cure’.
Arriving back at the mansion, The Doctor was too late to save Cynthia, one of Roley’s maids, from being killed by the patients, with Roley being driven mad when they rewrote his mind to match the program The Doctor had been running. Fortunately, Sam’s leech interfered with the others long enough for The Doctor to anaesthetise the patients while he carried out his own research. A leech was extracted from Fitz – Fitz having naturally inherited the gene from his mother , The Doctor was able to determine how to make telepathic contact with the Beast by using Sam and Fitz’s leeches as an interface. Communicating with the Beast directly, The Doctor was able to determine that they were typically harmless, feeding on the planet’s population but passing on without the inhabitants being aware of them; the destruction of Benelisa had only been an unfortunate accident due to Benelisa having too low a population to sustain the Beast’s feeding pattern. With this knowledge, The Doctor took the TARDIS to confront Azoth in his cave, but Azoth was too committed to his ‘crusade’ to listen to The Doctor’s argument that the Beast wasn’t evil, beginning preparations to initiate his ‘Final Solution’ – destroying all life on Earth to stop the Beast – before Fitz bluffed Azoth by claiming that he could destroy the Beast.
Returning to the mansion, The Doctor was too late to stop the patients from regaining consciousness, with his attempt to acquire a cure from Azoth’s memory banks backfiring when he had accidentally reactivated Azoth after determining a means of curing Sam. Azoth’s body was destroyed by Watson, but The Doctor was able to salvage his head, determining that the ‘Final Solution’ was a bioelectric pulse that would fry the brains of everything in the blast radius. Retreating to the wine cellar as a temporary barricade, The Doctor was able to rewire Azoth’s head to generate a pulse that would only affect those infected with the leech, unable to cure them and knowing that they were too dangerous to be allowed to continue after his attempts to reason with them failed. With the patients stopped and Sam cured, The Doctor and Sam departed, with Azoth’s head as a souvenir and Fitz as their new companion, and it left Roley to whatever medical treatment could do for him after the trauma of his experiences (Although they took a temporary detour to 2135 to confirm the Beast’s departure from Earth, The Doctor reasoning that the later Dalek invasion – “The Dalek Invasion of Earth” – would have depleted Earth’s population to a point where they couldn’t sustain the Beast if they had remained).