Radik

Radik was a Gallifreyan encountered by the Fourth Doctor and Romana I on the planet UX80 (or Cultura).

Biography
During his studies at the Prydonian Academy, Radik was kicked out for unauthorised radiation experiments before he could become a Time Lord. Stealing a TARDIS for himself, Radik fled to the planet UX80 and began his revenge against the Time Lords on the deserted planet.

Presumably having discovered Radik's plan, the Time Lords sent the Fourth Doctor and Romana I to UX80. Finding the planet ensnared in darkness, the duo used a wave translator to see. They very quickly found Radik's TARDIS. Radik then spoke to the Doctor and Romana, explaining his backstory to them. Romana was then attacked by a lump of gelatinous orange matter (presumably a creature used by Radik). The Doctor attempted to save Romana through a battle of minds but passed out.

Once the Doctor and Romana recovered, Radik claimed to have control over the duo's minds. Romana told the Doctor to keep Radik talking and used this distraction to destroy Radik with her sonic screwdriver. (PROSE: Light Fantastic)