K9 Mark III K9 Mark III was the designation given to the third known version of the robot K9 . This version was given by the Doctor as a present to his former companion , Sarah Jane Smith . The Doctor left him in a crate in her flat in Croydon in 1978 , but she did not actually open the crate until she visited Moreton Harwood in December 1981 . This model of K9 eventually broke down to the point of deactivation during his time alongside Sarah Jane , and sat motionless in an attic for many years because his futuristic inner - workings could not be shared with other humans . Though Mark III was later given the repairs he needed from the Doctor , he remained in poor condition and did not get to enjoy his reactivation for long . In a sacrificial final act , K9 Mark III valiantly gave up his life to eliminate a horde of Krillitane s preying on the human race . Biography . Travels with the Doctor and Adric . After the Doctor had left K9 Mark II to Romana as a gift , K9 Mark III travelled with the Doctor and Adric for a short time . ( PROSE : " Inter - Galactic Cat " , " Conundrum " , " Planet of Paradise " , " Plague World " , " Just a Small Problem " ) With Sarah . The Doctor left K9 for Sarah Jane Smith in 1978 at the only address he had for her : the home she had shared with her aunt , Dr Lavinia Smith , on Hill View Road in South Croydon . He left a message with K9 : he was to inform Sarah Jane that he was a gift from the Doctor and to " give Sarah Jane Smith my fondest love , tell her I shall remember her always . " ( TV : " The Hand of Fear " , " A Girl ' s Best Friend " ) Sarah Jane had already moved out of her aunt ' s home by that time and was travelling extensively . Unaware of its contents , Lavinia stored the shipping crate in her attic until 1979 . By then , she had purchased a manor house in Moreton Harwood and relocated there . She had the crate moved to the drawing room in anticipation of Sarah Jane ' s Christmas visit in 1981 , coinciding with her own departure for a lecture in the United States . Sarah Jane and her aunt ' s ward Brendan Richards discovered and opened the crate on 18 December 1981 . Two days later , K9 helped Sarah Jane defeat Moreton Harwood ' s Hecate Cult . ( TV : " A Girl ' s Best Friend " ) After this happened , Sarah , Brendan , Lavinia and K9 continued to investigate and stop other cults and witchcraft covens present in Britain . ( PROSE : " Powerstone " , " The Shroud of Azaroth " , " Hound of Hell " , " The Monster of Loch Crag " , " Horror Hotel " , " The Curse of Kanbo - Ala " ) " Circa " 1983 , K9 Mark III " lived " with Sarah Jane in a semi - detached house ; their gate bore a " beware of dog " sign . On one occasion , he warned her of impending danger somehow involving the Doctor . Sarah Jane dismissed his sense of danger , and declined to either stay home or take him with her . As a result , he did not accompany her as she was abducted to the Death Zone on Gallifrey . ( TV : " The Five Doctors " ) Later , K9 went with Sarah to an archaeological dig in Egypt . ( COMIC : " City of Devils " ) In the early 1990s , K9 assisted her in investigating a supposedly haunted house . ( PROSE : " Housewarming " ) In 1995 , K9 assisted Sarah Jane in contacting Alistair Gordon Lethbridge - Stewart with his large databank of telephone numbers . ( PROSE : " Downtime " ) In 1996 , Sarah used K9 to hack into records and find Sam Jones ' home address , and translate Lost Boy ' s speech . ( PROSE : " Interference - Book One " ) Breakdown . K9 was briefly possessed by a demonic pig spirit , but was freed when Sarah accidentally electrocuted him . ( PROSE : " The Sow in Rut " ) K9 began slowly breaking down and Sarah Jane was not able to replace K9 ' s failing recharging batteries and self - repairing systems . He spent months or years between times he was awake , and Sarah Jane abandoned him in a cardboard box behind a television set in her lounge . He was awakened by two burglar s lifting the box he was in . He immobilised the burglars with stun blasts and called the police before Sarah Jane got home , depleting the last of his emergency power and shutting down . ( PROSE : " A Dog ' s Life " ) Having essentially given up on being able to repair him , Sarah Jane relegated K9 to a cardboard box in her attic . ( PROSE : " Moving On " ) She w Later , Hilda Winters had K9 dismantled and analysed . ( AUDIO : " Mirror , Signal , Manoeuvre " ) Sacrifice . In early 2007 , Sarah Jane encountered the Doctor again , now in his tenth incarnation . He was able to repair K9 sufficiently to restore basic functionality , restricted to minimal power . He used K9 to identify the intelligence - enhancing oil used in a school ' s chips as Krillitane oil . When Mickey Smith woke K9 to break into the school during the ensuing fight with the Krillitane s , K9 pointed out they were in a car . Although Mickey did not immediately understand what K9 was suggesting , he eventually did . He drove the vehicle straight through the glass doors . As the Doctor , Rose Tyler , Sarah Jane , Mickey and Kenny were cornered by the Krillitanes , K9 rescued them through use of his laser . This delayed the Krillitanes until he ran low on power and was left alone . Short on power with only one shot of his laser remaining , K9 needed to be right next to a vat of Krillitane oil , which was now lethal to the Krillitanes , for " maximum impact " . As the Krillitanes closed in on him , their leader called him a " bad dog " after figuring out what he was about to do . K9 defiantly replied , " Affirmative . " He then blew up the school along with himself and the Krillitanes . Sarah was distraught when she learned what her robot companion had done , prompting the Doctor to design a new model which would carry on the memories of the old one . ( TV : " School Reunion " ) According to K9 Mark IV , as related to Sarah Jane , the Doctor rebuilt Mark III into Mark IV with " new omniflexible hyperlink capabilities " . ( TV : " School Reunion " ) From 2008 onward , Sarah Jane kept a photograph of K9 Mark III and her younger self on the wall of her attic study at 13 Bannerman Road , Ealing , along with portraits of Alistair Gordon Lethbridge - Stewart and Harry Sullivan . ( TV : " Invasion of the Bane " ) A different fate . According to another account , K9 stayed in the family for generations until he was inherited by a stockbroker named Frank in 4997 . Since neither Frank nor his fiancée Gloria were mechanically - minded , they decided to give it to Gloria ' s uncle , Professor Frederick Marius . The professor was amazed when examined the old machine , its technology being far in advance of the 20th century . However , Marius was forced to have it scrapped rather than take it with him to the Bi - Al Foundation due to shuttle weight restrictions . He watched as K9 was destroyed , compacted into a tiny metal square . He kept the motherboard as a memento , and later used it as the basis of a new computer which he had constructed at the Foundation , naming it K9 as well . . . ( PROSE : " Tautology " ) Features . Mark III included some improvements over past models . The new mechanics of K9 Mark III included larger wheels and a front and back - wheel drive . K9 also had a brand new coat of paint ( this time a metallic - blue ) , ( TV : " A Girl ' s Best Friend " ) though over time , Mark III rusted to some extent . The paint on his metal casing had faded and chipped away a bit by the time she brought him to the Tenth Doctor to restore some of his functionality . ( TV : " School Reunion " ) Mark III also had a handle on the top of the shell to make carrying him easier . ( TV : " A Girl ' s Best Friend " ) Although Sarah Jane indeed carried K9 Mark III to load him into and out of her car , ( TV : " A Girl ' s Best Friend " ) the Eleventh Doctor later implied that Mark IV was not the first to be capable of hovering . ( TV : " The Power of Three " ) 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 " ) K9 ran on an electron - fusion nuclear battery . Though K9 usually recharged himself when necessary , Sarah Jane had occasionally done so by clipping jump leads to his antennae . ( PROSE : " Housewarming " ) Technology . K9 was an advanced computer built in the shape of a robot dog . Among the technology included were a tri - state bus driver , a universal asynchronous receiver / transmitter and holographic memory . He was powered by a self - charging nuclear battery . K9 Mark III was 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 requested from his memory banks . ( TV : " A Girl ' s Best Friend " ) Behind the scenes . " K9 and Company " . 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 , but this element never made it to the screen . The idea of a mechanical companion to Sarah Jane being partially controlled by an enemy was recycled with Mr Smith in " The Sarah Jane Adventures " story " The Lost Boy " . A publicity photograph of Sarah Jane and K9 Mark III from " K9 and Company " was displayed in a pan across the 13 Bannerman Road attic at the start of " Invasion of the Bane " , being only the second use of classic era footage in the revived era , the first being a photo of Brigadier Lethbridge - Stewart an instant earlier .