K9 Mark II

K-9 Mark II was the second K-9 based on a robot originally build by Professor Marius, though constructed by the Doctor.

History
Mark II was constructed as a replacement for the Doctor after Mark I, decided to stay on Gallifrey with Leela (DW: The Invasion of Time)

This version of K-9 accompanied the Doctor and new companion on their quest to locate the segments of the Key to Time (DW: The Ribos Operation), however the swampy terrain of Delta III made it impossible for him to accompany them there. At the conclusion of the quest, the Shadow turned K-9 to his evil will, during which time K-9 assumed a sinister personality. (DW: The Armageddon Factor)

The Doctor found that K-9 had contracted laryngitis and had lost his voice as a result of this. K-9 was left in the TARDIS while the Doctor and Romana battled the Daleks and Davros (DW: Destiny of the Daleks). During a subsequent adventure, it remained patiently in the TARDIS, which would imply that his voice had not yet returned. (DW: City of Death) After the return of his voice, it sounded quite different and remained so for a number of adventures (DW: The Creature from the Pit). However, later the familiar voice returned. (DW: The Leisure Hive)

Damaged by the time winds, K-9 Mark II could not cross back into N-Space with the Doctor, so decided to stay behind at the Gateway with Romana, to help her free the remaining Tharils from slavery. (DW: Warriors' Gate)

He was later repaired, and accompanied Romana when she returned to N-Space. During Romana's term as President of Gallifrey, K-9 Mark II served as her aide and advisor. (NA: Lungbarrow) He may have also shared an adventure with Romana and later incarnation of the Doctor at some point after this (WC: Shada)

Features
After K-9 Mark I was left behind with Leela on Gallifrey, The Doctor built an improved K-9 Mark II. While the cosmetic changes were minimal (including the new metallic charcoal paint-work), in terms of series continuity K9's character underwent a vast change. Gone was the product of 5000 AD technology, as was the case with Marius's version. This new K9 was a product of the Doctor's own technology and values. The gun was now only capable of stunning - not killing - and K-9 now responded to a dog-whistle. K-9 also featured a vast memory-bank, seemingly a mixture of the Mark One model, the Doctor's own memory and knowledge, and that of the TARDIS. (DW: The Invasion of Time)

Production notes
The production team used the same prop for Mark II as they had for K-9 Mark I.

Casting
While John Leeson provided K-9 Mark II's stories in all his other appearances, another actor, David Brierley voiced him in The Creature from the Pit, Nightmare of Eden and The Horns of Nimon. Leeson took over the role again from The Leisure Hive onward.