Primord

The Primords were savage 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 came into contact with Stahlman's ooze. The transformation occurred in stages. First the infected area turned green, then spreading across the entire body. Their faces developed bestial qualities and teeth changed into fangs. Strength is drastically increased, as shown when one effortlessly bent the bars of its prison cell. They began to generate heat in a way impossible for a human. Once full 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.

Behaviour
Primords banded together in groups and instinctively sought to force humans into physical contact with the ooze that they would themselves transform. They could survive great heat and even gunshots 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. (DW: 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.

Stahlman himself was converted after he touched a fractured glass containing the ooze. His transformation complete while he was in the drilling room. He was disabled by the Third Doctor and Greg Sutton with fire extinguishers. (DW: 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. (MA: The Scales of Injustice)

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 and the Primords already created forced others into the ooze so that they changed. Despite the efforts of the Third Doctor and a parallel Greg Sutton, the Primords took over the drilling facility. This was followed shortly be a flow of lava from the core that destroyed the planet. (DW: Inferno)

Behind the scenes

 * The name "Primord" (from "primordial") comes from the closing credits, promotional and reference material to Inferno. It does not occur in the story itself at all.