Harry Slocum was a maintenance worker at the Inferno Project.
While repairing a drill pipe, he was infected with Stahlman's ooze and rapidly mutated into a Primord. His killing of a fellow worker soon caused UNIT to be brought in to investigate. Later, the creature that had been Slocum knocked out Bromley, infecting him, and increased the Project's power output to maximum. When Slocum confronted the Third Doctor, Private Wyatt shot Slocum twice through the heart, killing him, but not before Wyatt became infected himself. (TV: Inferno)