Thawn is one of the secondary antagonists (alongside Ranquin) of the 1978 Doctor Who serial "The Power of Kroll".
He was portrayed by Neil McCarthy.
Thawn was the head of a refinery that dealt with various mineral resources found on the third moon of the planet Delta Magna. The refinery was staffed by him, fellow humans Fenner, Harg and Dugeen, and Mensch, a slave belonging to the native "Swampie" tribe. As the swampies were opposed to the refinery, Thawn sought to exterminate them, but in a way that would seem justified in case of insurrection from humanitarian groups.
To this end, Thawn made a deal with arms dealer Rohm-Dutt to sell the swampies faulty weapons, giving Thawn an excuse to wipe them out. However this plan was complicated when the swampies captured Rohm-Dutt. A further complication arose when Thawn and Fenner found the time traveller known as The Doctor wandering the marshes. Believing him to be a spy, they shot him with a stun gun and captured him, but he slipped away relatively easily.
After Dugeen discovered a huge creature on the scanners, Thawn and Mensch went out into the swamp to investigate and find the Doctor. The swampies ambushed them and opened fire with the weapons Rohm-Dutt gave them, but as they were faulty all they achieved was dying when the weapons exploded. In the ensuing confusion, Kroll, the monster Dugeen had seen, arose and dragged Mensch away to his death, forcing Thawn to retreat.
However, soon after Kroll attacked the refinery and killed Harg. In response, Thawn prepared a missile strike to wipe out the swampies, hoping it would kill Kroll as well. Dugeen objected to Thawn's plan and attempted to stop the countdown, so Thawn shot him dead. Fenner turned on him for this, calling him a murderer.
The Doctor returned to the refinery, intending to stop the countdown. Thawn caught him in the act and prepared to execute him, but was stopped when the swampies took advantage of the damage Kroll did to the refinery to attack. Thawn was caught by surprise and was easily killed by a spear.