M is for... Mutants

Every 500 years, the humanoid inhabitants of the planet Solos underwent a strange metamorphosis. This was a natural mutation, triggered by seasonal changes. Hard, black, scaly skin developed, and the Solonians became more violent and aggressive in the initial stages. They then transformed into bipedal insectoid creatures.

At this point, they were compelled by instinct to seek out radiation-rich caverns. Their ancestors had placed a special crystal here, which aided the mutation process through to its final form - when the Solonians became ethereal super-beings.

Around the 25th Century, Solos fell under the domination of the Earth Empire, and exploited for it radioactive minerals. Efforts by its governor - the Marshal - and an incompetent scientist to change Solos' atmosphere to make it breathable to humans inadvertently triggered the process prematurely. Thinking of them as nothing more than animals, and believing the mutation to be a communicable disease, the Mutants were hunted and killed. The rest took shelter in the cavern near the cave of the crystal.

Another human scientist named Sondergaard attempted to show that the creatures were intelligent and harmless, but his efforts failed. The young rebel leader Ky underwent the transformation, rapidly passing through the Mutant phase to emerge as a super-being. He killed the Marshal, freeing his people. Sondergaard would then help other Mutants transform fully.

When a Mutant landed on the storm-lashed planet of Karn in an escape pod, it was quickly attacked and killed by Condo - servant of the surgeon Mehendri Solon. He sought out survivors of the frequent spaceship crashes for body parts which could use in his master's medical experiments. The Doctor described the corpse as a Mutt - member of a mutant insect species from the Cyclops Nebula.

Played by: John Scott Martin, Laurie Goode, Mike Mungarvan, Eddie Sommer, Nick Thompson Hill, Ricky Newby, Bill Gosling, Mike Torres. 

Appearances: The Mutants (1972), The Brain of Morbius (1976).

• John Scott Martin played the lone Mutant in the Tom Baker story, as well as lead creature in the Pertwee one.
• It is simply the case of a reused costume for The Brain of Morbius (helmed by the same director, Chris Barry), as the Doctor's description does not really match with the Solonians.
• The costume designer is future Oscar-winner James Acheson.