K9 Mark IV K9 Mark IV was an intelligent robot in the form of a dog that was a companion of Sarah Jane Smith and subsequently Luke Smith , also serving as their beloved pet . He was a gift from the Tenth Doctor to Sarah Jane to replace his previous model . Biography . K9 Mark IV was the fourth in the line of K9 robots . He was based upon the original K9 Mark I designed by Professor Frederick Marius in 5000 , and which travelled with the Fourth Doctor and Leela . ( TV : " The Invisible Enemy " ) Sometime after she had stopped travelling with him , the Doctor had gifted K9 Mark III , an improved version of the first two K9s , to his former companion , Sarah Jane Smith . ( TV : " A Girl ' s Best Friend " ) Mark III was eventually destroyed fighting off a Krillitane invasion , and so Mark IV was presented to Sarah Jane as a replacement by the Doctor , by then in his tenth incarnation . ( TV : " School Reunion " ) The Eighth Doctor had previously mentioned a Mark IV version . ( PROSE : " Interference - Book Two " ) K9 said that the Tenth Doctor rebuilt him with " new omniflexible hyperlink capabilities " . ( TV : " School Reunion " ) Sarah Jane wasn ' t able to enjoy Mark IV ' s company for long . Soon after being presented to her ( approximately a year - and - a - half before Sarah Jane first met Maria Jackson ) , K9 Mark IV was forced to enter deep space in order to stabilise a dangerous artificial black hole in space which had been created in Switzerland . She lamented being all alone . ( TV : " Invasion of the Bane " ) K9 was able to maintain occasional communication with Sarah Jane via a cabinet with a space - time link when the orbit of the black hole intersected with that of Earth . ( TV : " Invasion of the Bane " ) At times he was capable of returning to Earth briefly , and did so on several later occasions in order to render vital assistance . He fought Mr Smith in pitched battle to allow Sarah Jane to upload the Armageddon virus . ( TV : " The Lost Boy " ) He was later called back in order to quickly upload the TARDIS ' base code to Mr Smith , thereby assisting the Tenth Doctor in returning Earth to its correct location in space . ( TV : " Journey ' s End " ) After each of these events , K9 went back into space to continue monitoring the black hole . Some time later , a member of the Slitheen family attempted to steal him as part of a revenge plot against Sarah Jane . K9 banished the Slitheen , after reversing one of its attacks . ( TV : " From Raxacoricofallapatorius With Love " ) Later , Sarah Jane transferred the black hole into fuel for Eve ' s Ship . K9 then triumphantly returned to the Smith house ( 13 Bannerman Road , Ealing ) to stay . He greeted Mr Smith — who held something of a resentment towards him — and had a photograph taken with Luke Smith , Clyde Langer and Rani Chandra . In 2059 , Rani still had that photo . ( TV : " The Mad Woman in the Attic " ) He then helped defeat Travast Polong and the Trickster after reuniting with the Tenth Doctor . ( TV : " The Wedding of Sarah Jane Smith " ) A drawing of him by Clyde was animated by alien energy and defeated the Abomination . ( TV : " Mona Lisa ' s Revenge " ) He later assisted in tracking down a pair of Slitheen , locating them with his " olfactory sensor s " . ( TV : " The Gift " ) When Luke Smith was trapped in a nightmare by the Nightmare Man , K9 , with the help of Cention Concrete , managed to transport himself into Luke ' s nightmare . Soon after , K9 was temporarily damaged by the Nightmare Man . ( TV : " The Nightmare Man " ) He aided invaluably in the defeat of Ruby White by resetting the Qetesh ' s artificial intelligence , allowing Luke to take control of it . ( TV : " Goodbye , Sarah Jane Smith " ) Although Sarah Jane had appeared unconcerned with K9 Mark III being seen when they lived together twenty - five years earlier , she restricted Mark IV to their house except in the case of emergencies or as needed , lest she have to explain him . Luke covered by claiming K9 to be a Japanese robot toy with pre - programmed phrases . ( TV : " The Wedding of Sarah Jane Smith " ) Nevertheless , she sent him to care for Luke when the latter left for the University of Oxford . ( TV : " The Nightmare Man " ) He stayed in Oxford when Luke returned home in 2011 , but Luke had taken K9 ' s whistle just in case . Luke later used the whistle to contact Mr Smith , which helped defeat John Harrison . ( TV : " The Man Who Never Was " ) Personality . Unlike his previous model , this K9 seemed slightly more capable of having and understanding emotion . Such examples are that he did not reject Sarah Jane ' s affections when she was concerned for him , and his constant rivalry with Mr Smith for the best technical support . Another was that he possessed a sense of right and wrong , instead of simply obeying orders — for example , when Clyde tried to use K9 ' s knowledge to help him pass a test at school . K9 tended to give long - winded explanations to why he was behaving in an unusual manner , only to have someone correctly give a simpler way of explaining it . ( TV : " The Gift " ) Features and improvements . This K9 had a shiny metallic blue paint job and a number of improvements over Mark III including an omniflexible hyperlink facility ( TV : " School Reunion " ) and universal serial bus ports . ( TV : " The Nightmare Man " ) Later , though , K9 reverted to his old , dark green colour . ( TV : " Invasion of the Bane " ) In his battle with Mr Smith , K9 displayed a teleport facility and utilised a laser weapon similar to the previous K9 models . ( TV : " The Lost Boy " ) Upon receiving him , Sarah Jane changed his collar colour to nearly match the pattern on the Fourth Doctor ' s scarf , the same or identical collar to those worn by the previous K9s . Unlike his previous models , although like K9 Mark 2 , K9 ' s eyepiece could glow at night . ( TV : " The Lost Boy " ) He also had a compartment in his side , which could hold items , such as the sonic lipstick s and the scanner watch , which were gifts from the Tenth Doctor to Sarah Jane after their last meeting . ( TV : " Invasion of the Bane " ) Whereas earlier K9s including Mark III were seen being lifted into , out of , and over things , K9 Mark IV had a hover mode , enabling him to negotiate the stairs in the Smiths ' three - storey house and multi - level attic , and to access and egress automobiles on his own . ( TV : " The Wedding of Sarah Jane Smith " , " The Gift " ) K9 claimed that he was shaped like a dog because " the human ego requires a familiar reference point to aid in adjusting to new concepts . Animal forms are comforting to the majority of humans . " ( PROSE : " Housewarming " ) Behind the scenes . SJA appearances . The reason for K9 ' s fleeting appearances in " The Sarah Jane Adventures " was due to other parties holding the rights to the character , for use in a spin - off TV series , " K9 " , although the character had not been completely forbidden from appearing in " The Sarah Jane Adventures " . As , in the first episode of the K9 series , K9 Mark I was destroyed in a self - sacrifice and " regenerated " into an entirely redesigned model and the TV series bought the rights to the concept and simply " borrowed " the character and , briefly , original design , with full consent , the rights to the character and design of the original K9 once again belong to the BBC who could use K9 ( as per his original design ) freely in " The Sarah Jane Adventures " . His minor appearances up until that time had been simply to be careful not to misuse the rights allowance whilst they were still being decided upon .