Balor

Balor is an alien from the planet Progron, found imprisioned in a rogue asteroid made of living rock.

History
At least a thousand years prior to his encounter with Moonbase Alpha, Balor's people had achieved immortality by artificial means, and over time their society became corrupt and started to decay. Together with others, Balor had tried to reverse the process, and help his people find the meaning of life, only for them to turn on him, and condemn him to an eternity of solitude within an asteroid of living rock.

On February 2001 Balor was recovered by the inhabitants of Moonbase Alpha. When the Alphans realise Balor intends to keep them alive to torture them, following the death of Mike Baxter, they resist him, with Commander Koenig eventually ejecting Balor out of an airlock, and ordering the asteroid destroyed.

Biology
Balor's immortality is due to accelerated cell regeneration with no time to decay (in the script it is undetectably slow except in his wounds, i.e. the speed of cell regeneration varies according to need). Many cells have a timer that limits the numbers of divisions; also each regeneration may accumulate errors in DNA replication. Some animals can regenerate limbs or tails, by growing a blastema, an amorphous mass of undifferentiated cells that migrate to the wound and specialise into functional tissues. Evidently Balor's genetic code has been reprogrammed to do the same. Electrical stimulation can aid the process of cell regeneration; note Balor also has an electric touch that he uses for torture.