Thomas Bruce was a CIA agent.
He was ordered by Control to acquire secure files from UNIT and cause as much damage as possible while doing so. Under the name Bruce Davis, he pretended to be a liaison from the American branch of UNIT. After he completed his assignment, including killing a UNIT technician and disfiguring the body with acid to make it look like he was the victim, Bruce went to the coast and escaped via hovercraft.
When the Brigadier was captured, he was brought to Bruce, who took him back to America and turned him over to Control. After the Waro threat was stopped and the Nedenah who had helped left Earth, Bruce found evidence in the files he had stolen that his son's leukemia had been caused by his ex-wife's exposure to Nedenah technology whilst she was pregnant. Grief-stricken at this realisation, he attempted to commit suicide, but Control prevented him from doing so, mockingly telling him that he joined the CIA for life and they wouldn't allow him to leave that 'easily'. (PROSE: The Devil Goblins from Neptune)