K9 Mark I

K9 Mark I was a portable computer originally owned by Professor Marius, who considered the robot dog his "best friend". Together, they conducted advanced medical research at the Bi-Al Foundation for an unknown length of time. When the Fourth Doctor and Leela arrived at the Foundation, Leela quickly became enamoured of the dog. The professor eventually gave the dog to the time travellers as thanks for defeating The Swarm. (TV: The Invisible Enemy)

The Mark I was particularly associated with and protective of Leela. Therefore, when she elected to remain on Gallifrey, he also chose to stay behind with her. (TV: The Invasion of Time) Nevertheless, he occasionally left Leela's side when he was sent on solo missions by the Time Lords. During these adventures he travelled in a spacecraft the Time Lords build especially for him called K-NEL. (PROSE: K9 and the Missing Planet, and others)

He eventually came into the service of Lady President Romana II when Romana tapped Leela as her personal bodyguard. Together, Leela and the Mark I went on many missions together at Romana's request. He was a vital link between the two ex-companions of the Doctor, since he could easily and silently interface with Romana's K9 unit. (AUDIO: Square One and others)

The unit's ultimate fate was considerably unclear, since two radically different accounts existed. According to one, he was utterly destroyed in an explosion and Leela adamantly refused to have another model built in its place. (AUDIO: Imperiatrix) The other held that he somehow ended up on 21st century Earth, where he was forced to engage his regeneration unit and become K9 Mark 2. Thereafter he accepted a boy named Starkey as his new master, and had several adventures on Earth in the 2050s. (TV: Regeneration)

Later models — or marks — of K9 were based on this one.

Creation
It was unclear who, exactly, invented the K9 "concept". When he first met Leela, Professor Marius said only that he "had K9 made up" — not that he "created" or "designed" the unit – because weight restrictions did not allow him to bring his real dog from Earth into space. (TV: The Invisible Enemy)

One account claimed that K9 may have owed his existence to a temporal paradox. Far from inventing the dog himself, the professor copied the remnants of one of the versions of K9 created by the Doctor and given to Sarah Jane Smith. (PROSE: Tautology)

Meeting the Doctor and Leela
In the year 5000 AD, K9 aided Marius in scanning the Fourth Doctor for the Swarm inside him. He later fought off the humans infected by the Swarm on Bi-Al and on Titan Base, saving the Doctor and Leela's lives on several occasions.

The Professor offered K9 to the Fourth Doctor to travel in the TARDIS as the same weight restrictions made him unable to take Mark I back to Earth with him. (TV: The Invisible Enemy)

Sometime during his travels, he met Robin Hood. (TV: The Last Oak Tree)

The Doctor arrived on Agratis to see the Jewel of Fawton and eat a banquet. However, the Jewel had gone missing, and the Judoon had been called in to reclaim it. While the Doctor searched for the Jewel's thief, Leela and K9 distracted the Judoon out of the city so the Doctor could leave; K9 connected himself to a tank, and Leela hijacked a motorbike.

When the species that originally owned the Jewel were discovered, the Judoon's search was called off. Becoming much less aggressive, Leela invited them to dine at the banquet. While Leela was feasting with the Judoon, a mysterious cloaked figure kidnapped Leela and K9. (COMIC: Prisoners of Time)

On the TARDIS
After a number of adventures with Leela and the Doctor, Mark I decided to stay on Gallifrey with his "mistress". (TV: The Invasion of Time)

On Gallifrey
Though K9 remained on Gallifrey to "protect" Leela, he was occasionally used by the Time Lords for various solo missions. Towards this end, they gave him a specially built space vessel called K-NEL that only he could control, which gave him freedom of movement in space, but not time. (PROSE: K9 and the Time Trap, et al)

K9 was briefly reunited with the Doctor, now in his seventh incarnation, who stopped by to see how Leela's development had progressed. The Doctor took the identity tag from K9's collar as a memento to remember him by. (PROSE: Affirmative)

K9 was with Leela on Gallifrey for many years, but it was only after the disappearance of her Time Lord husband, Andred, that she and her K9 met Romana II and her K9. Despite the fact that the two K9 units did not get on well and competed with each other, (AUDIO: Weapon of Choice, The Inquiry) they frequently networked together and allowed easy communication between their respective mistresses. (AUDIO: Square One)

After Leela became Romana's bodyguard, and after many important missions on her behalf, Leela's K9 was destroyed in a bomb explosion, leaving Leela heartbroken, but refusing to allow a duplicate unit to be built in its place. (AUDIO: Imperiatrix)

After being destroyed
In a way not clearly understood, K9 Mark I survived the explosion that Leela and Time Lord technology confirmed had utterly destroyed him. It is possible that Romana rebuilt him at some point, as a thank you present to Leela.

At some point after this event, and indeed after the Last Great Time War, he became an agent of the Korven. (TV: Hound of the Korven) During this period, he had a number of adventures whose details were not well recorded. For example, the Mark I was known to have gone to the second planet of the Montoon system and observed the Sea of Brains. (TV: Curse of Anubis) He also liberated the Anubians from the Huduct. (TV: Curse of Anubis)

Regeneration
Later, he went to the year 50,000 and met Zanthus Pia, head of the Galactic Peace Commission, whom he later saw murdered at the hands of Ahab, a Jixen emissary and his three guards. As K9 was a witness, the Jixen attacked K9. (TV: The Bounty Hunter) The Jixen were pulled to 2050 London via a Space-Time Manipulator and tried to warn the humans about a Korven invasion. However, they couldn't speak English and the humans believed they were attacking them. K9 came through the STM and attacked the Jixen. After a brief battle he realised his power was running low, and as a last resort to protect the humans, K9 self-destructed, destroying himself and two of the Jixen. Although working for the Korven, he cared for the safety of humans and advised them to evacuate. Using his regeneration unit, the remains transformed into a new incarnation. (TV: Regeneration, Hound of the Korven)

Personality
K9 was often left behind in the TARDIS and so he saw journeying out as a treat. (TV: The Sun Makers) He stated that to wish was to have emotion and so he wished for nothing. Despite this he regularly showed emotion, even sulking when shouted at. The Doctor described him as overbearing, arrogant and insufferable, after K9 told him there was only a 1% chance of the Doctor having a better explanation for something than him. (TV: The Invasion of Time)

Features
The mechanics of K9 Mark I included rotating ear-probes, telescopic 'eye' probe, extendable nose, flashing lights on the top and the 'eye' panel, waggling tail antennae, and ticker-tape tongue. The head could also move up and down. The shell was painted in gold/grey metallic. There was a monitor screen on his left flank, though K9 rarely used this during his travels with the Doctor. Around K9's neck was a tartan collar, from which hung a silver disk. (TV: The Invisible Enemy) By the time of his liberation of the Anubians, K9 was modified (likely by the Time Lords or the Korven) so he could fly through the vacuum of space. (TV: Curse of Anubis)

Behind the scenes

 * In an early draft of The Invisible Enemy, K9 was called FIDO, for "Phenomenal Indication Data Observation". (INFO: The Invisible Enemy)
 * The original K9 model was designed by visual effects designer Tony Harding. One early concept was to have a small actor in a large Doberman-shaped costume; however, Graham Williams vetoed this, saying that the robot should not look like a person in a costume. The eventual design was closely based on Harding's third concept sketch. (DCOM: The Invisible Enemy)
 * K9 Mark I was the first in a seven-year run of non-human televised companions who inhabited the TARDIS, ending with the departure of Turlough in 1984. Others included K9 Mark II, Romana I, Romana II, Adric, Nyssa and, nominally, Kamelion.