K is for... Kiv

A mutant member of the Mentor race, from the planet Thoros Beta. His enhanced mental abilities allowed him to process the planet's economy, ensuring wealth for the avaricious species. However, his mutation had a drawback. His brain had developed to a point where it threatened to outgrow his cranium.

A corrupt scientist named Crozier was employed by the Mentor Sil to save the life of his leader.

Kiv decreed that if he failed, both would die. Crozier set about conducting experiments with a view to transplanting Kiv's brain into a new body with a larger cranium. The humanoid inhabitants of nearby Thoros Alpha were considered, but none were suitable as a host.

A side-line of his work was the manipulation of the brains of others, to make them more amenable to the Mentor's financial schemes. This was attempted on the warrior king Yrcanos, but failed.

As a temporary measure, Crozier transplanted Kiv's brain into the body of a marine cousin of the Mentors. This was a more primitive sub-species, which retained its toxic sting.

Crozier decided not to transplant the brain again, as he had discovered a means to transplant only the contents of the brain - the mind of Kiv, with all its memories and personality.

The body selected to host Kiv's mind was that of Peri, the Doctor's companion. Yrcanos had fallen in love with Peri, and when he discovered what Crozier had done he killed Kiv, along with Crozier and Sil.

It later transpired that this event had been fabricated by the Valeyard, and Peri had survived. The true fate of Kiv is unknown.

Played by: Christopher Ryan. Appearances: Trial of a Time Lord (Parts 5 - 9 - AKA Mindwarp) (1986).

• Ryan rose to fame as one of The Young Ones - Mike the Cool Guy.
• He returned to Doctor Who in 2008 to play General Staal in The Sontaran Stratagem / The Poison Sky. Two years later he played another Sontaran in The Pandorica Opens.
• In the final episode of Trial of a Time Lord we learn of Peri's survival, but we are never told at what point the events seen within the Matrix diverge from what actually happened.