Harry Slocum is a minor villain in the Doctor Who serial Inferno. In both realities, he is a mild-mannered technician who is tragically turned into a monster. He is played by Walter Randall.
Harry Slocum was a technician working at the Inferno Project. He was called in by Sir Keith Gold to repair a damaged coolant pipe in the drill housing. While working, he discovered a mysterious green ooze seeping up from the pipe and touched it. He thereafter began turning into a Primord. After beating another technician to death with a wrench, he went to the nuclear reactor's power station where he attacked scientist John Bromley and knocked him out. He then started turning the reactor's power up to maximum in the hopes of increasing the heat.
The Doctor investigated, bringing Brigadier Lethbridge-Stewart, Sergeant Benton and Private Wyatt of UNIT with him. The four encoutered Slocum, who snarled at them and refused to allow them near the controls for the reactor. While the Doctor distracted him, Wyatt shot Slocum, but this initially didn't seem to do any good, and the enraged Primord attacked the private, knocking him out, before finally succumbing to his bullet wounds and dying when the Doctor managed to restore the power to normal.
Slocum isn't seen in the alternate reality, but he did exist in it. Presumably, the alternate universe's version of Harry Slocum was similar to if not identical to the first. He was a technician who worked at the Inferno Project and turned into a Primord, attacking three people before being killed by Republican Security Force troops.