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Characters / Doctor Who – K9

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K9 Mark ISpelling  (Fourth and Tenth Doctor)
First appearance: "The Invisible Enemy" (1977)
Voiced by: John Leeson (1977–78, 2009)

"Affirmative master!"

The first robot-buddy of the franchise, hailing from the 51st century. K-9 Mark I, the original built by Professor Marius, was a highly advanced robot built to resemble a dog. Known for his laser nose, propensity to speak in Literal-Minded terms, and his constant uttering of "Affirmative", or "Negative", which stuck with his descendants. He had a short run and remained with Leela on Gallifrey. This was because his prop's maintenance sucked. Prone to break even if it hit a simple bump on the floor, he was quickly replaced by Mark II. Mark I was later brought back in his own series but due to design copyrights, he got destroyed in a fight with the Jixen and regenerated through a special repair unit into a brand new appearance with Laser-Guided Amnesia to sever all explicit ties with the Doctor Who franchise.

Tropes associated with the television continuity

Doctor Who

  • Badass Adorable: K9 is treated like a cute little dog by the Doctor (when the Doctor isn't grumbling over K9 being smarter than him), yet nonetheless is a capable thinker who can use his laser nose to easily stun enemies and destroy objects. This is best shown in "School Reunion", where K9 is doted on like a house pet by the Tenth Doctor yet nonetheless is the one who saves the day in dramatic fashion thanks to his cunning and his laser beams.
  • The Blank: His face can't express any emotion at all, but his rotating "ears" and waggly tail can give himself away.
  • Breakout Character: Like Sarah Jane, he got two spin-off television series, even if they were shortlived.
  • The Cameo: The original K-9 hosted the 40th anniversary celebrations for the series while it was in its so-called wilderness years, voiced by John Leeson.
    • The newly-introduced Mark IV, also played by Leeson, appeared on The Weakest Link in 2007 for a promotion of Series 3, but he was mostly a Joke Character who was voted off immediately. The reason was that the prop operators feared K-9's dreaded habit of breaking down at the most inconvenient times would happen during the game, so they made sure he would be voted off in the first round (the game's selection of DW cast itself admittedly agreed to rig their votes so that only members of the regular cast at the time were guaranteed to stay on till the final round and guest cast got the boot—but this didn't stop top-billed actors from being voted off).
    • Also cameoed on Queer As Folk as the perfect gift for Doctor Who fan Vince, an Author Avatar in this respect of Who fan and future New-Who re-creator and showrunner Russell T Davies.
    • Blatant Lies/The Time Traveller's Dilemma: Cameoed on an episode of Jim'll Fix It. invokedIn order to prevent Reapers from destroying London on account of a temporal paradox, had to pretend to be "pleased to meet Mr. Savile and chair".
  • Canine Companion: The Doctor insisted on treating him like an actual dog.
  • Character Catchphrase: "Affirmative." "Negative." "Master/Mistress?"
  • Cute Machines: He is very adorable.
  • Deadpan Snarker: He got into many a snarking match with Four.
  • Do-Anything Robot: Laser beam, hacking computers, defensive protocols, beating the Doctor at Chess, being a Deus ex Machina...
  • Family Friendly Firearm: K-9's ever-convenient laser beam has a kill option, but is always set on stun.
  • Hypercompetent Sidekick: Particularly if viewed specifically as The Doctor's sidekick.
  • Insufferable Genius: He's a futuristic alien super computer, so he's just as smart as the Doctor. And he's well aware of it.
    The Doctor: We all make mistakes sometimes, don't we, K9?
    K9: Negative.
  • Kid-Appeal Character: K-9 was a huge hit with children, which contributed to his longevity as a companion despite the notoriously unreliable prop being a constant thorn in the production staff's side.
  • Made of Iron: Subverted, K9 gets damaged often despite his claims of not being made of tin.
  • Non-Human Sidekick: Serves as a beeping Robot Buddy for The Doctor in the original series.
  • Only Sane Man: K9 seems to cater to this. Being The Spock of the team, focusing on logical reasoning in everything he does, his clinical nature is a far cry from the Doctor's eccentricity and the quirks of his various companions.
  • Pint-Sized Powerhouse: His laser weapon helps him take care of opponents often twice his size.
  • Punny Name: Get it? K-9? Because it looks like a dog! K-9! As in CA-NINE.
  • Robot Buddy: To the Doctor, Romana, Leela and Sarah Jane.
  • Robot Dog: A medical robot, originally.
  • The Spock: Being a medical robot at heart, K9's programming prioritizes logical reasoning first and foremost, never acting on impulse and rebutting the Doctor's own rash decisions.
  • Smart People Play Chess: In "The Sun Makers", K9 plays chess with the Doctor, with the latter attempting to show that his intellect is superior to any computer. K9 ends up winning anyway, with the Doctor too caught up in his own smugness to believe it.
  • Zeerust: His appearance would have been considered fairly tacky and retro even by the show's standards when he was first introduced. It's eventually lampshaded in "School Reunion".
    Rose: It looks so... disco.
    Tenth Doctor: Oi! In the year 5000 this was cutting-edge!


Tropes associated with Big Finish

Voiced by: John Leeson

  • The Comically Serious: Sarcasm is completely lost on him, and would react to snarky remarks from the Doctor and his other companions at face value. Hilarity frequently ensues.
  • Brainwashed and Crazy: K-9 in Return to Telos when under Cyber-control.
  • Grand Theft Me: He's temporarily taken over by Zodaal in "The English Way of Death".
  • The Mole: When infiltrating the Rocket Men.
  • No Social Skills: He's basically a talking calculator on wheels and the one thing going for K-9 is that everyone thinks he's cute.
  • Not Now, Kiddo: A running gag with the Fourth Doctor, who'd tell K-9 to be quiet just before k-9 has something important to tell him.
  • One-Steve Limit: Discussed with the Doctor, when he gets very confused as to why K-9 refers to both The Doctor and The Master as "Master". He tells K-9 to call The Master "The Renegade".
  • Only Sane Man: Likes to think of himself as this, but his complete lack of understanding humans leads to very awkward (and funny) situations, and averts this trope.
  • Robot Buddy: At least on the occasions when he leaves the TARDIS at all.
  • Sliding Scale of Robot Intelligence: Frequently displays Level 4 abilities in episodes like "Requiem for the Rocket Men", where he's able to do dozens of mathematical equations simultaneously in his head while assisting the Doctor in about three other difficult tasks.

K9 Mark II

First appearance: "The Ribos Operation" (1978)
Voiced by: John Leeson (1978, 1980–81, 1990, 1993); David Brierly (1979–80); Roy Skelton (1979)

K-9 Mark II was the replacement for Mark I, who would now only stun, not kill things (at least not living things - he does kill at least one robot). Affectionately referring to the Doctor as "Master", Mark II was conceived because K-9 was popular with the kids, but the prop needed a redesign after breaking down all the time. He stayed with Romana II when she stopped travelling in the TARDIS. John Leeson quit the role at the end of Season 16, so David Brierly was brought in for Season 17 as his interim voice actor. The change in his voice was Hand Waved as K-9 contracting robot laryngitis. Brierly quit after on season and Leeson returned for Season 18, on the understanding that K9 would be written out during the season.

Tropes associated with the television continuity

  • Badass Pacifist: In keeping with the Doctor's morals, this K9's potentially lethal nose-laser was dialled down to only having a stun setting.
  • Literal-Minded: More so than the Mark I.
    Romana: Uh, K-9, what is tennis?
    K9: Real, lawn or table, mistress?
    Romana: Never mind. Forget it.
    K9: Forget. Erase memory banks concerning tennis. [whirring sound] Memory erased.
  • Replacement Goldfish: After K9 Mark I elects to stay with Leela on Gallifrey, the Doctor casually starts unpacking a boxed Mark II that he apparently kept around in case of this eventuality.

Tropes associated with Big Finish

Voiced by: John Leeson

K-9 travels with the Doctor, and Romana, but has on occasion been relegated to looking after the TARDIS while his Time Lord friends go out exploring. He eventually joins back up with Leela and Romana in the Big Finish spinoff Gallifrey. On one occasion, both K-9 and Romana, after establishing themselves on Gallifrey, rejoin with the Doctor for a once-off adventure involving Professor Chronotis.

K9 Mark III

First appearance: "Doctor Who Annual 1982: Inter-Galactic Cat" (1981)
Voiced by: John Leeson (1981, 1983, 2006)

K-9 Mark III was the model who got given to Sarah Jane Smith as a gift from the Doctor, in the One-Episode Wonder K-9 and Company. He turned up in a few comic stories and "The Five Doctors", and that was it (unless you count the non-canon "Search Out Space" and "Dimensions in Time"). He didn't appear again until 2006 in a few audio stories leading up to Sarah Jane Smith's return to the series proper, where he got badly damaged, fell into disrepair, and rusted in Sarah Jane's attic because she didn't know how to fix a robot dog with futuristic technology, nor could she reveal said technology to anyone before its time. Mark III's functionality was somewhat restored by the Tenth Doctor, long enough for him to give his life by defeating the Krillitanes.

Tropes associated with the television continuity

K9 & Company

Doctor Who

  • Awesomeness by Analysis: The Tenth Doctor and Sarah-Jane repair him so he can figure out what's on with the chips at a school they're investigating. Once he's fixed up, he works it out quickly.
  • The Cameo: Briefly appears during "The Five Doctors", when we see Sarah-Jane leaving for work.
  • Deadpan Snarker: What does he suggest Mickey do to break into the school?
  • Heroic Sacrifice: Blows up a bunch of Krillitane oil tanks, but in order to do so has to be right by the barrels.
  • Spin-Offspring: Mark III's first appearance was in an obscure comic story and he prominently appeared alongside Sarah Jane in a failed spin-off pilot. His only appearances in the main TV series were a brief cameo in "The Five Doctors" and a more major role in "School Reunion".
  • Took a Level in Badass: Thanks to an improved special effects budget, K9 gets to zap multiple Krillitane when he reappears in "School Reunion".
  • Used Future: Unfortunately has this aesthetic by the time of his return in "School Reunion" thanks to years of neglect (which was justified since the Doctor gave Sarah Jane no maintenance equipment and the technology used to build K9 is several centuries too advanced).
  • Zeerust: His retro-futuristic appearance is mocked by Rose and defended by the Doctor as "cutting edge" for the 51st century.

K9 Mark IV

First appearance: "School Reunion" (2006)
Voiced by: John Leeson (2006, 2007, 2008, 2009-2010)

K-9 Mark IV was given to Sarah Jane by the Tenth Doctor as a replacement for Mark III, along with a sonic lipstick inside his casing. Mark IV was better associated as Sarah Jane's K-9 than the Doctor's, and this loyal robot called her "Mistress". He sported a more computerized-sounding voice and did not have as many locomotion woes because he could hover up stairs. He served as Sarah Jane's loyal pet and had an ongoing rivalry with Mr. Smith, the Xylok supercomputer. However, licensing issues left him trying to close a black hole after a Switzerland experiment went awry for the first three seasons of the The Sarah Jane Adventures. Then, he had a more active role in the plot, until the Australian K-9 series came out and the licensing disputes resurfaced, causing him to go to college with Luke Smith and return to light roles in the show.

Tropes associated with the television continuity

Doctor Who

  • Big Damn Heroes: During "Journey's End", since the Doctor has forgotten the TARDIS base code, Sarah-Jane calls K9 out to provide it.
  • The Nth Doctor: While physically distinct, he's treated as being the same individual as Mark III as he has retained all of the previous model's memories.

The Sarah Jane Adventures

  • Big Damn Heroes:
    • His cameo appearances prior to joining the regular cast mostly consisted of him teleporting in when Sarah calls for him to save the day, most notably at the end of Series 1.
    • Luke and Clyde take advantage of this by bringing to life Clyde's highly detailed drawing of K9 to help fight off the Mona Lisa and the Abomination (it's a long story).
  • Commuting on a Bus: Spends most of Series 1 in the aforementioned black hole plugging situation, but afterwards he increases in prominence, alternating between being a regular and a Drop-In Character.
  • Put on a Bus: Leaves to accompany Luke to university. (Out-of-universe, written out due to rights issues following the beginning of the Australian K-9 TV show.)
  • Replacement Goldfish: A positive depiction. He was specifically created by the Doctor as a gift to Sarah Jane to fill the void left by K9 Mark III, but thankfully Sarah Jane's relationship with Mark IV is just as close as with Mark III.
  • Sesquipedalian Loquaciousness: Lampshaded on several occasions.
    K-9 (In reference to Mr Smith): Contact with that computer interferes with this unit's synaptic circuits.
    Clyde: You mean he gets on your nerves.
    K-9 (More assertively that normal): Affirmative.
  • Sitcom Archnemesis: He doesn't like Mr. Smith and the feeling is very much mutual. The two seem to compete for Sarah Jane's affections in the same way as rival housepets. Their ongoing enmity could be partially justified by lingering distrust after Mr. Smith's Face–Heel Turn incident which led to them having an intense firefight in the attic.
  • Spock Speak: "Affirmative Mistress".

K9 Mark 2

First appearance: "Regeneration" (2009)
Voiced by: John Leeson (2009-2010)

Tropes associated with the television continuity

  • The Nth Doctor: Largely subverted in that, while each K-9 unit is essentially the exact same thing as the previous model, the version in the K-9 spinoff looks and acts drastically different.
  • Spock Speak: Subverted, unusually enough. This K9 is actually capable of normal, modern-sounding slang.


Video Example(s):



As the Krillitanes attack, K9 shoots down one of them with his blaster. The Doctor tells K9 to hold them off while they retreat.

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Main / BadassAdorable

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