Primord

The Primords (AUDIO: Primord) were savage, furry humanoids created by Stahlman's ooze. They existed in both the Doctor's universe and a parallel universe visited by the Third Doctor.

Transformation
Primords were humans who had come into contact with either Stahlman's ooze or another infected human. The transformation occurred in stages. First, the infected area turned green, then spread across the entire body. The infected human's face developed bestial qualities and his teeth changed into fangs. Strength was drastically increased, as seen when one effortlessly bent the bars of its prison cell. Primords could generate heat in a way impossible for a human. Once fully transformed, they grew thick hair and partial hunchbacks. The transformation process took several hours under normal conditions, but in heightened temperatures, the full transformation could occur in a few seconds. (TV: Inferno)

Behaviour
Primords banded together in groups, and instinctively sought to force humans into physical contact with the ooze so that they too would transform. Although a partially converted human could be killed by gunshots, once fully transformed into a Primord, they were immune. They could survive great heat, but found cold temperatures, such as those generated by fire extinguishers, to be fatal. Upon entering a room, they would sometimes need time to acclimatise to the temperature. (TV: Inferno)

The Doctor's universe
The first Primord was Harry Slocum, who came into contact with Stahlman's ooze while performing maintenance on the drill. It took him several hours to transform and even then it wasn't complete. In this time he accessed the power supply and almost caused an overload.

Before Slocum was killed, he infected John Bromley and Private Wyatt. Wyatt later fell to his death while trying to kill the Third Doctor and Bromley was killed when the Doctor sprayed him with a fire extinguisher.

Stahlman himself was converted after he touched a fractured glass tube containing a sample of the ooze. His transformation became complete while he was in the drilling room. He was killed by the Doctor and Greg Sutton with fire extinguishers. (TV: Inferno) C19 preserved a small sample of the ooze in the Vault, injected it into a Dobermann Pinscher, and used it to create a mutated guard-dog known as the Stalker. (PROSE: The Scales of Injustice)

The Primords were finally given a name by Michael, who took the name from the word "primordial". When General Sharp and Lady Madeline Rose decided to explore the possibility of weaponising the Primords, they recruited Liz Shaw's help in modifying the ooze to accelerate the rate of infection and eliminate some of the Primords' weaknesses. However, they were unaware that Liz had been contaminated by the ooze during her work, which drove her to try and perfect the plan only so that she could unleash the Primords herself. She was able to infect the Doctor to enlist his 'help', but the Doctor managed to suppress the infection long enough to tell the Brigadier and Jo Grant how to help him, allowing him to keep his temperature down long enough to find an antidote that could be distributed in a liquid form, which he released into the sprinkler system of the school where he was carrying out his work. (AUDIO: Primord)

Parallel universe
The Third Doctor visited a parallel universe where the same drilling operation was occurring. The drilling released a significant amount of the ooze. The Primords which had already been created forced others into the ooze, so that they changed as well. Despite the efforts of the Third Doctor and a parallel Greg Sutton, the Primords infested the facility shortly before the planet was devastated by volcanic activity triggered by the drilling. (TV: Inferno)

Behind the scenes
The name "Primord" (from "primordial") originated from the closing credits, promotional and reference material to Inferno. It did not occur in the story itself at all. In-universe, the species' name was first given in the audio story Primord.

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