K9 was the designation given to a series of intelligent, dog-like robots who served as companions of Professor Marius, the Fourth Doctor, Leela, Romana, and Sarah Jane Smith.
K9 Mark I, II, III, and IV addressed whoever was directing them as “Master” or “Mistress” depending upon gender, and used the formal “affirmative” and “negative” rather than “yes” and “no”. They were programmed to be both loyal and logical, with a penchant for taking orders literally, almost to a fault. Their striped collars mirrored the Fourth Doctor’s trademark scarf.
K9 had a personality very consistent across the models with some contact with the Doctor. He was polite and formal, with pedantry bordering on condescension. Though he often displayed feelings such as sorrow and self-regard, he often stated that he had not been programmed to have emotions.
He did not use contractions such as “you’ve” for “you have” and addressed others by titles such as “Master”, “Mistress”, “Doctor-Master” (to refer to the Doctor) or “Young Master” (Adric). Though he did not seem to resent his subordinate status, he sided with the Doctor’s companions over the Doctor and showed a dark side, regarding other artificial intelligences with contempt.
With his great intelligence, he had a tendency to bore people with facts and did not stop immediately when asked, as he did to Leela on Pluto. When being told that he would have to stay behind in the TARDIS, K9 often argued, giving the Doctor reasons why he should go such as “he would be a good dog.” K9 always wanted to assist the Doctor.
K9 Mark I
Professor Frederick Marius, who invented the first K9 in the year 5000 while working on the asteroid K4067, described him as “my best friend and constant companion.” Marius had a dog on Earth, but weight requirements did not allow him to bring his real dog into space, so he built K9. Marius used his own medical computer, a state-of-the-art intraresponsive brain app, protective anti-radiation cladding, probes, a laser scalpel, a vision and voice box and two scanning antennas.
The Professor offered K9 to the Fourth Doctor as the same weight requirements made him unable to take Mark I back to Earth. After adventures with Leela and the Doctor, Mark I decided to stay on Gallifrey with his “mistress”.
- The Invisible Enemy (from Part 2)
- Image of the Fendahl
- The Sun Makers
- The Invasion of Time
K9 Mark II
The Doctor obtained or constructed at least one backup model of K9. Immediately after leaving Mark I behind with Leela, he unpacked K9 Mark II. This version of K9 accompanied the Doctor and his new companion on their quest to locate the segments of the Key to Time.
This K9 exhibited the ability to sense and warn others of danger. He was also more mobile than his predecessor.
K9 travelled to E-Space with the Fourth Doctor and Romana II, where they met Adric. Damaged by the time winds, K9 Mark II could not cross back into N-Space with the Doctor. He decided to stay behind at the Gateway with Romana II to help her free the remaining Tharils from slavery.
- The Invasion of Time (Part 6, boxed)
- The Ribos Operation
- The Pirate Planet
- The Stones of Blood
- The Androids of Tara
- The Armageddon Factor
- Destiny of the Daleks
- The Creature from the Pit
- Nightmare of Eden
- The Horns of Nimon
- The Leisure Hive
- Full Circle
- State of Decay
- Warriors’ Gate
K9 Mark III
A third model, K9 Mark III (again either obtained or constructed by the Doctor), was shipped in 1978 to Sarah Jane Smith at the home she had shared with her Aunt Lavinia in South Croydon during her companionship of the Third and Fourth Doctors (A Girl’s Best Friend).
After several adventures, K9 Mark III slowly began breaking down and eventually ended up deactivated in a cardboard box in Sarah’s attic. When the Tenth Doctor met Sarah Jane, he reactivated K9 and made temporary repairs. However Mark III ended up sacrificing himself whilst fighting strange, bat-like creatures.
As a heartbroken Sarah Jane watched the Tenth Doctor depart, the TARDIS dematerialised to reveal Mark IV. K9 said the Doctor rebuilt him with “new omniflexible hyperlink capabilities”.
- A Girl’s Best Friend (K9 and Company)
- The Five Doctors
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