G is for... Gastropods

An ancient legend on the planet of Jaconda told of how its ruler had offended the Sun God. They sent a swarm of giant slug-like creatures to lay waste the planet to punish the people. Many centuries later, this legend proved to have been based on a real event, as one of the creatures hatched out - Mestor. Soon the whole planet was overrun with the creatures - Gastropods - and Mestor seized control from the rightful ruler. This was an elderly Time Lord named Azmael, who had once been an old friend of the Doctor. The Jacondans were enslaved, and the population began to starve as the Gastropods once again laid waste to their crops. Mestor maintained control thanks to powerful mental capabilities, such as telekinesis. He could even place his mind into the bodies of others. He told Azmael that he had a scheme to move two other worlds in the Jacondan solar system into orbit around the planet, so that they could be used as new food sources. To achieve this, Azmael was sent to abduct twin boys from Earth - Romulus and Remus - who possessed the mathematical skills to achieve this. The newly regenerated Doctor and his companion Peri gave chase, along with an Earth security officer named Hugo Lang.

On discovering that Mestor had amassed a huge number of Gastropod eggs, with especially hardened shells and which responded to heat, the Doctor spotted his real scheme. The two smaller planets would fall into Jaconda's sun, resulting in an explosion which would destroy the planet. The eggs would survive - flung out into space to colonise other worlds. The Doctor prepared an acid to attack Mestor. The Gastropod ruler transferred his mind into Azmael's body, however, unaware that he was close to death. The Doctor destroyed his original body, and the old Time Lord died, no longer able to regenerate. Mestor was expelled. The other Gastropods did not share his mental powers, and the Jacondans rose up against them - led by their new ruler, Hugo.

Played by: Edwin Richfield (Mestor). Appearances: The Twin Dilemma (1984).

• Richfield had previously appeared in the series as Captain Hart in The Sea Devils.
• Mestor's "spirit" is seen to emerge from Azmael as he dies. As he can inhabit other people's bodies, he may have simply transferred to a nearby host and so may have actually survived.