Thorn (The Bounty of Ceres)

 was a technician who was part of the crew on Ceres.

He looked after the First Doctor after he was exposed to subzero temperatures. After seeing that the oxygen creation algae was dying he initially thought of letting the Doctor die and putting Vicki Pallister and Steven Taylor in cryo storage to conserve oxygen.

The Doctor eventually deduced that Thorn had caused the problems by tracing the start of the original errors to the times when Thorn had been the only member of the crew active while out of direct contact with Earth. Considering Moreland an idiot, Thorn had planted a series of subtle subliminal programming cues intended to psychologically undermine Morland, eventually reaching a point where Thorn's induced errors included hull breaches, computer malfunctions and the maintenance robots going haywire. After the Doctor, Steven and Vicki arrived, Thorn's subtle changes escalated due to the addition of three other people, resulting in the death of Qureshi before his plans were exposed. Faced with arrest, Thorn deliberately threw himself out of a door that vented into space. (AUDIO: The Bounty of Ceres)