- You may be looking for the Wyatt of the Inferno universe.
Wyatt was sent with the Third Doctor to a nuclear power plant after there was a power surge at the Inferno Project. There they encountered the Primord which had been Harry Slocum. Wyatt fired twice into its heart. However, the Primord's natural resistance allowed it to hit Wyatt before dying. This hit infected Wyatt and he began to mutate into a Primord.
The Doctor spotted Wyatt running from him and gave chase. He followed Wyatt through the power plant and caught up with him. Wyatt turned and attacked the Doctor with the butt of his gun, but the Doctor dodged the swings. Wyatt overbalanced and fell over a rail to his death. A soldier approached the corpse but the Doctor shouted instructions that he was not to be touched lest he be contaminated. (TV: Inferno)