K9 Mark I

K9 Mark I was built by Professor Marius to accompany and assist him in his work at the Bi-Al Foundation. He served as the template for all future versions of K9.

On the TARDIS
Professor Marius invented the first K9 because weight requirements did not allow him to bring his real dog from Earth into space (DW: The Invisible Enemy) though K9 may owe his existence to a temporal paradox. According to one account, the professor copied the remnants of one of the version of K9 created by the Doctor and given to Sarah Jane Smith. (DWM: Tautology)

The Professor offered K9 to the Doctor as the same weight requirements made him unable to take Mark I back to Earth with him. (DW: The Invisible Enemy) After a number of adventures with Leela and the Doctor, Mark I decided to stay on Gallifrey with his "mistress". (DW: The Invasion of Time).

On Gallifrey
There are (possibly apocryphal) accounts that this model of K9 later performed missions on behalf of the Time Lords and was given control of a space vessel called K-NEL (The Adventures of K9: K9 and the Time Trap, et al).

K9 accompanied Leela on Gallifrey for many years, but it was only after the disappearance of her Time Lord husband, Andred, that Leela and her K9 met Romana and her K9 (the two K9 units did not get on well and competed with each other). (BFG: Weapon of Choice) 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. (BFG: Imperiatrix)

Later Life
K9 Mark I is known to have survived the Last Great Time War, despite have been destroyed earlier. Some point later he went to the year 50'000 and met Zanthus Pia Head of the Galatic Peace Commission who he saw murdered at the hand of Ahab. Being a witness to the murder Ahab's Jixen friends attacked K9 (K9TV: The Bounty Hunter). He and the Jixen was pulled to mid-21st century Earth via a Space-Time Manipulator, after a brief battle he self-destructed to save the Humans in the are both destroying himself and the Jixen (bar one). Unlike other K9 models, Mark I had by this time been equipped with a regeneration circuit which allowed him to be recreated as a new model. (K9TV: Regeneration)

Undated events

 * Travels to the second planet of the Montoon system and observed the Sea of Brains.(K9TV: The Curse of Anubis)
 * Liberates the Anubians from the Huduct .(K9TV: The Curse of Anubis)
 * Meets Robin Hood. (K9TV: The Last Oak Tree)
 * K9 had a vast database inherited by his next incarnation containing data on the following aliens.
 * Jixen
 * Meron
 * Korven
 * Oroborus

It is unknown wether he acutally encountered any of these species before he encountered them as K9 Mark 2.

''These events could have occured between the end of the Last Great Time War and his Regeneration or on his missions for the Time Lords. All of the undated events apart from the liberation of the Anubians could have also occured in his travels with the Doctor.''

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. Around K9's neck was a tartan collar, from which hung a silver disk. (DW: The Invisible Enemy) By the time of his liberation of the Anubians, K9 was modified (likely by the Time Lords) so he could fly through the vacuum of space. (K9TV: The Curse of Anubis)

Behind the scenes

 * K9 Mark 1 returned in the first episode of K9 (TV series). Bob Baker had said that the K9 model that appears in the early part of the first episode is "identical to the one Leela had in Gallifrey". This means K9 Mark 1 has survived the Time War.
 * Although another actor's voice was heard as K9 in the new series' promotional trailer, it was later confirmed that John Leeson would once again perform the character's choice for the TV series.