K9 Mark III

K9 Mark III was the designation given to the third known version of the K9 robot. This version was given by the Doctor as a present to his former companion, Sarah Jane Smith.

History
How Mark III came to be built has not been chronicled. Based upon the original K9 Mark I designed by Professor Marius (DW: The Invisible Enemy), and upon K9 Mark II, which the Doctor, in his fourth incarnation, was shown uncrating following the decision by Mark I to stay on Gallifrey (DW: The Invasion of Time), it is assumed that Mark III was either built by the Doctor, or he obtained it from the same source from which he obtained Mark II.

Travels with Sarah Jane Smith
The Doctor left K9 for Sarah Jane in 1978, but she did not actually learn of its existence until 1981. Soon after being uncrated, K9 assisted Sarah Jane in defeating the Hecate Cult of Moreton Harwood. (KAC A Girl's Best Friend) It is known that K9 and Sarah Jane shared more adventures after this, but only a few have been chronicled. (K9 Annual 1983, et al)

Circa 1983, K9 Mark III still lived with Sarah Jane, but, by chance, did not accompany her to Gallifrey. (DW: The Five Doctors) Later, K9 accompanied Sarah to an archaeological dig in Egypt. (DWM: City of Devils) In the early 1990s, K9 assisted Sarah in investigating a supposedly haunted house. (VD: Housewarming) In 1996, Sarah used K9 to hack into records and find Sam Jones' home address, and later to translate Lost Boy's speech. (EDA: Interference - Book One)

Break down
K9 was briefly possessed by a demonic pig spirit, but was freed when Sarah accidentally electrocuted him. (ST: The Sow in Rut) K9 began slowly breaking down and eventually ended up deactivated in a cardboard box in Sarah's attic. (VD: Moving On) Hilda Winters later had K9 dismantled and analysed. (BFSJS: Mirror, Signal, Manoeuvre)

Sarah Jane began carrying K9's remains around in the boot of her car, having given up on being able to repair him with modern-day technology. (DW: School Reunion)

Sacrifice
In 2007, when Sarah Jane met the Doctor again, he successfully repaired K9. During the ensuing incident with the Krillitanes, K9 oddly bonded with Mickey Smith, who identified himself as being another of the Doctor's "tin dogs". K9 Mark III ultimately sacrificed itself to stop the Krillitanes, which led to emotional reactions from both the Doctor and Sarah Jane.

Not long after, however, the Doctor presented Sarah Jane with K9 Mark IV, and the two went off for more adventures. (DW: School Reunion

Features
Mark III included some improvements over past models. The new mechanics of K9 Mark III included larger wheels in conjunction with a front and back-wheel drive. K9 was also given a brand new coat of paint (this time a metallic-blue) and a handle on the top of the shell to make carrying him easier. (KAC: A Girl's Best Friend)

Technology
K9 was an advanced computer built into the body of a robot dog, among the pieces of technology included in his construction were a tri-state bus driver, a universal asynchronous receiver/transmitter, holographic memory, and was powered by a self-charging nuclear battery. Also programmed with a wide variety of technical knowledge and scientific data which included, among other things, horticulture. K9 could also provide data printouts of any information required from his memory banks (KAC: A Girl's Best Friend)

Behind the scenes

 * Only the pilot episode of K9 and Company, A Girl's Best Friend, was ever aired.
 * In the original outline to K9 and Company, it would have been eventually revealed that K9 Mark III was actually sent by and under the control of the Master, but this element never made it to the screen.