The many, many people who accompany the Doctor in the Doctor Who revival series (2005 onwards). For their ongoing character tropes in Big Finish Doctor Who (in which the original actors continue to play them), see here.
Warning: There are a lot of unmarked spoilers on this page. Proceed with caution.
Mickey Smith (Ninth and Tenth Doctors)
Young Mickey played by: Casey Dyer (2005)
- "Me? I'm their 'man in Havana', their technical support... Oh God, I'm the tin dog."
Mickey starts the show as Rose's boyfriend, abandoned by her when she became the Doctor's companion. This doesn't stop him from running around for a few adventures during that series anyway, although he and Rose never quite manage to patch things up. He later joins the TARDIS crew as a companion for a few episodes early in the second series, only to stay behind off-planet (sort of). He returns at the end of the second series, as well as the end of the fourth and briefly in the 2009 specials. In the end, he found true love and married Martha Jones.
- All Love Is Unrequited: Played straight with Rose, later averted with Martha, whom he married.
- Alternate Universe: His counterpart in the zeppelin world is a gay gangster named Ricky. (The gay part is suggested from a deleted scene, but it's debatable if the scene is canon or not.)
- Always Second Best: He can't measure up to the Doctor even after taking his level in badass. Eventually, he stops trying to and decides to become his own person. Leading him to look for his own purpose in life, away from the TARDIS and Rose.
- Badass Beard: Once he starts fighting aliens freelance.
- Badass Normal: A powerless human that eventually becomes a cybermen slayer.
- Black and Nerdy: He's a more than capable hacker.
- Butt-Monkey: The Doctor considers him an idiot, his girlfriend gives him little to no respect, his girlfriend's mother accuses him of murder when her daughter goes missing, Jack starts making fun of him within ten seconds of meeting him, and even K-9 gets to throw in a bit of snark while informing him, "We are in a car." Hell, his own parallel-universe equivalent finds him embarrassing, and this is a guy who considers himself a badass because of the number of parking tickets he's accrued.
- Childhood Friends: Rose and Mickey were this before they started dating at some point before the start of the series. This is why theyre still emotionally attached to each other after they break up and why Mickey is so close with Jackie.
- Humiliation Conga: His girlfriend runs off with an alien after basically snarking how useless he was. She goes missing for a year and the police haul him in five times, while her mother and the entire estate gives him hell about it. The Doctor keeps calling him Ricky and turning into better looking guys while hauling his girlfriend all over the cosmos. Then Mickey pisses on everyone and decides to show his worth.
- I Choose to Stay: At the end of "The Age of Steel", he stays behind in the alternate universe to help his dead alternate self's boyfriend (long story) fight the Cybermen and take care of his parallel-universe grandmother. Then he comes back for good at the end of "Journey's End" (after returning briefly in "Army of Ghosts" and "Doomsday").
- I Want My Beloved to Be Happy: Once it becomes clear that Rose has chosen the Doctor and doesn't see a future with him, Mickey is still willing to help her get back to the Doctor if that's what she truly wants.
- Know When to Fold 'Em: Carries a torch for Rose for years despite her affections for the Doctor, but as soon as the Metacrisis Doctor is sent to live with Rose and company in Pete's World, returns to the prime universe. Between this and his parallel-universe grandmother having passed away, Pete's World no longer has anything to offer him.
- Love Triangle: Rose leaves him as soon as she meets the Doctor, although she considers herself "sort of" Mickey's girlfriend for a while after that. When she also starts fancying Jack, Mickey pretty much gives up on the relationship. He becomes part of the family again when he and Rose are left without the Doctor for a few years, but eventually steps out of her life forever when Rose gets together with the Doctor's half-Donna clone.
- The Mole: He manages to infiltrate Torchwood 1, after learning that the Cybermen of Pete's World had managed to cross universes. They never caught on.
- My Greatest Failure:
- He's felt guilty for not helping his grandmother fix the stair carpet, which caused her to fall and break her neck. He decides to not let that happen again when he sees her parallel counterpart and decided to take care of her until she passed away peacefully.
- Also when his counterpart Rickey was deleted, he decided to not let it happen again.
- Nice Guy: A pretty laid-back boyfriend, if a bit aimless... at first.
- Pair the Spares: With Martha Jones, offscreen.
- Parental Abandonment: His father Jackson Smith was a locksmith who just took off one day when Mickey was a kid. The series never states where Mickey's mother is, but the novelization of "Rose" mentions she committed suicide. He was largely raised by his grandmother, who while genuinely loving also tended to slap him a lot.
- Poke the Poodle: His parallel equivalent is London's Most Wanted... For parking violations.
- Punny Name: Perhaps not intentional, but to "take the mickey" out of someone is to take any fight/vigor/self importance out of them by mocking them, and Mickey does have to put up with a great deal of mockery and bullying from Rose and the Doctor (mostly Nine, but Ten has his moments), and Jackie at first.
- Rebel Leader: Alternate Mickey. (It's Ricky.)
- Refusal of the Call: Initially, after his help in "World War Three", the Doctor offers him a spot in the TARDIS only to be turned down (one of the few companions to do so).
- Replacement Goldfish: Becomes one for Jake, Ricky's boyfriend. Jake copes pretty well with the idea, but since Mickey's not gay, it's a dysfunctional setup to say the least.
- Salt and Pepper: Alongside his partner in crime, Jake.
- Taking Up the Mantle: When his alternate self dies, Mickey simply assumes his identity and continues the fight.
- Techno Wizard: He describes himself as "technical support" because he's very good with computers.
- Token Minority Couple: With Martha, of the "Independently-Made" variety.
- Took a Level in Badass: Multiple. To wit, from lovable but aimless boyfriend to a capable hacker and fully-fledged companion. Ends up fighting Cybermen in an alternate reality and respected member of that reality's Torchwood, and finally earns his happy ending with a woman who saved the world with the power of story.
Adam Mitchell (Ninth Doctor)
Short-lived companion; a Teen Genius from 2012. Holds the dubious honour of being the only companion to be evicted from the TARDIS for bad behaviour.
- Arbitrary Skepticism: Has a job that revolves around the collection of alien artifacts, but sees alien abduction stories as nonsense.
- Big Bad: For Prisoners of Time.
- Butt-Monkey: He doesn't get a lot of respect.
- Ditzy Genius: A teen genius who thinks that his plan to sell information back to his own time is a good idea.
- Jerkass: Intentionally written as a troublemaker to show what kind of person makes for a bad companion.
- Insufferable Genius: Very smug about it.
- The Resolution Will Not Be Televised: Shows up again in the comics as an elderly man to show what happened to him after being left behind by the Doctor. It isn't pretty at all, and Adam's enormously pissed.
- Shoo Out the New Guy: Invoked. He's an example of what not to do if you're traveling with the Doctor.
- Teen Genius: And quick to mention it.
- Time Travel for Fun and Profit: Attempts to change his own future by sending information back from the year 200,000. It doesn't end well.
Wilfred Mott (Tenth Doctor)
A newspaper salesman from 21st century Chiswick, London. Originally a one-off character in "Voyage of the Damned", Wilfred was eventually revealed to also be Donna Noble's grandfather (a last-minute rewrite due to the actor hired to play Donna's father dying). This resulted in quite a few recurring roles throughout the fourth series, leading to fan-favourite status for the character and finally full-fledged companion status in "The End of Time", the Tenth Doctor's final story.
- Ascended Extra: Originally intended to be named "Stan" for "Voyage of the Damned" and never show up again. This changed when Howard Attfield, the actor playing Donna's father, passed away and Wilf was written in as Donna's grandfather.
- Badass Normal: Dalek. Paintball gun. It didn't work, but that's still quite a few levels of badassness above the norm.
- Catchphrase: "It's them aliens again!"
- Chekhov's Gun: Owns one, and convinces the Doctor to accept it as a gift.
- Cool Old Guy: Willing to do anything to save the world.
- Like a Son to Me: Despite being the Doctor's junior by more than 800 years.The Doctor: I'd be proud.
The Doctor: If you were my dad.
- Manly Tears: His friendship with Ten is very emotional.
- Missed Him by That Much: For all his talk about the aliens, when the Adipose ship is hovering over London, horns blaring all the way, Wilfred is too busy stargazing elsewhere through his telescope to notice, listening to music on a pair of headphones.
- More Expendable Than You: He tried to talk the Tenth Doctor out of his Heroic Sacrifice because he knows that the Doctor is a hero on a grand scale and he himself is just an old human man. The Doctor's response is basically, "No, you're not."
- Older Sidekick: Obviously more than qualifies in the real world; he's more than twice David Tennant's age. In fact, Bernard Cribbins is the oldest actor to have played a companion on the show, and had already appeared as a companion in the Daleks' Invasion Earth: 2150 A.D. film in 1966, five years before David Tennant was born. In-universe, the Doctor is still much older.
- Parental Substitute: Is this to Donna. After her father died, and given her mother's aloofness, she always turns to "Gramps". In "The End of Time" he also takes on some of these traits with the Doctor.
- Promoted to Opening Titles: For the Tenth Doctor's final story.
- Properly Paranoid: Firmly believes in alien visitors to Earth. Since he lives in the Whoniverse, boy is he right.
- Prophecy Twist: "He will knock four times." The Doctor was absolutely sure that it referred to the Master (and, admit it, so were you). Instead, after the Master is defeated, Wilf politely knocks four times on the door of his glass cage, hoping the Doctor will let him out.note Wilf previously trapped himself in the cage to save a random guy's life. The only way the Doctor can get him out is by killing himself.
- A Real Man Is a Killer: Defied he refuses to be ashamed of never actually killing during his military service.
- Retired Badass: He served in Palestine when he was younger, though by his own admission never took a life while there.
- Weapon of Choice: A paintball gun or his old service revolver. That works, too.
Craig Owens (Eleventh Doctor)
Rented a room out to the Doctor in "The Lodger" when the latter was stranded on Earth by a malfunctioning TARDIS. Hilarity Ensued. As Amy Pond was in the malfunctioning TARDIS and thus also separated from the Doctor, Craig had to act as a makeshift companion for him. As a result of a hasty Mind Meld Info Dump, he got the Doctor's memories beamed directly into his brain, and knows more about the Doctor's general history than most characters. The Doctor has come to view him as a very good friend. Craig returned in "Closing Time", this time in a more clear (if still brief) companion role, helping the Doctor defeat the Cybermen.
- Accidental Pervert: Comes off this way in the lingerie department in "Closing Time", resulting in Kelly calling security on him.
- Adorkable: Especially in "Closing Time", with his fatherly bumbling and comical failure to investigate.
- Always Someone Better: The Doctor to Craig, with regards to football and his job. Probably not the best thing to do to your landlord.
- Ambiguously Bi: He casually tells the Doctor that he's always welcome to bring over a girlfriend or boyfriend, and his only objection to the Doctor trying to snog him (It Makes Sense in Context) is that he's already taken. He and the Doctor get Mistaken for Gay by just about everyone, and while he finds it aggravating, it is, again, because he's already spoken for.
- Badass Normal: Emphasis on the latter to justify the former. He's so ordinary that a Lotus-Eater Machine exploded instead of killing him, and he once blew up an entire Cyberman base by simply letting them feel the mental feedback of his intense desire to protect his infant son.
- Badass Unintentional: None of the Badass Normal stuff he did was on purpose, and he was for the most part scared out of his mind.
- Breather Episode: Both "The Lodger" and "Closing Time" were low intensity and largely comical episodes between big and heavy stuff.
- Cannot Spit It Out: Craig and Sophie, even though Everyone Can See It, they can't admit to it until the end of their first episode.
- Charm Point: For the Doctor. Lampshaded that their relationship is similar to people opening up to talk to Craig whenever he brings his baby with him.The Doctor: That's why I usually take a Human along with me.
Craig: So I'm your baby?
The Doctor: You're my baby!
- Exposition Beam: The Doctor gives him one during "The Lodger". One headbutt for general context and then a second for details about the current crisis. It gives them both significant headaches.
- I Don't Want to Ruin Our Friendship: Craig and Sophie for most of "The Lodger"; they eventually decide to ruin their friendship properly. In their next episode, they have a child.
- Mistaken for Gay:
- The Doctor and Craig. As Val tells them, "There's no need to be coy these days." Val has more reason than most do for this trope, what with the way Craig and the Doctor act throughout the episode. She sees them hug, and they refer to each other as their "partner". Also, the Doctor tries to kiss Craig, but (as usual) that was to save their lives.
- Craig also makes it a point to make no assumptions about the Doctor when they first meet, telling him that he's always welcome to bring over a girlfriend or a boyfriend.
- Nice Hat: When the Doctor says he is going to America, Craig gives him the Stetson as a parting gift.
- Only Sane Man: Often points out how completely mental being around the Doctor is.
- Papa Wolf: Fatherhood stresses him out, but it also inspires him to fight Cyberman conversion.
- Power of Love: "I blew them [Cybermen] up with love!"
- Running Gag: The Doctor "Shhh"-ing people, and Craig wanting to be taught how.
- Stout Strength: According to the Doctor, he had to be pretty strong to keep the Cybermat from biting him.
- Too Spicy for Yog-Sothoth: Craig is so happy in his mundane life that it overloads the alien spacecraft in "The Lodger". In "Closing Time", his paternal instincts overload the Cybermen's emotional inhibitors, blowing up their whole ship.
- Unwanted Assistance: The Doctor's attempts to help Craig (joining his football team, filling in for him at work when he's sick, trying to get Sophie to admit that she loves him, etc.) just make him look like the better man who's driving Sophie away.
- Use Your Head: In order to save time explaining why he's staying with Craig, the Doctor headbutts him twice.
- Vitriolic Best Buds: With the Doctor. Craig may express exasperation, terror and irritation whenever the Doctor shows up, but it's clear he's secretly having the time of his life.
- Wrong Genre Savvy: Played With. Craig recognises that everywhere the Doctor goes, disaster will come... and also that the safest place for him and Alfie is by his side, because the Doctor always wins. While this seems to be a rather dubious assumption, but then again he has had the concise summary of the Doctor's life downloaded into his brain, which probably includes just how far the Doctor will go to protect a child, so he may not actually be wrong. Plus, safety around the Doctor is a rather relative term.
Nardole (Twelfth Doctor)
A timid, unassuming Human Alien of the 54th century who was a servant of River Song during her caper to reclaim a valuable diamond from (the head of) the tyrannical cyborg King Hydroflax, whom she'd recently married to get close to. On Mendorax Dellora in 5343, he was sent to fetch the surgeon River hired to perform the... "operation"... and a misunderstanding meant that he brought back the Twelfth Doctor. Long story short, by the end of this misadventure Hydroflax himself was destroyed and Nardole's head just the head, mind was peacefully sharing and controlling his deactivated robot body with that of Ramone, one of River's many husbands and also involved in the scheme; together they served as a waiter at a restaurant near the Singing Towers of Darillium. However, during the long night the Doctor spent with River on Darillium (long as in equivalent to 24 Earth years) he "reassembled" Nardole into a cyborg.
Before River went to her death in the Library, she tasked Nardole with becoming the Doctor's "valet"; he promised to take care of the Doctor, to keep him from losing his sense of self and his noble morals... by any means needed, up to and including kicking his arse. Thus, he followed the Doctor to what was to be the execution of Missy, and from there they took to guarding the Vault beneath St. Luke's University on Earth. Nardole is determined to make sure the Doctor holds to his vow to watch over Missy for 1,000 years, but this becomes harder when, several decades into the vigil, the Doctor meets and befriends Bill Potts.
- All There in the Manual: Paul Cornell's "Twice Upon a Time" novelization reveals he gets a Surprisingly Happy Ending post-"The Doctor Falls": He lives to over 700 years old on the colony ship, successfully defending the solar farmers against the Cybermen often enough that at last they only have to deal with with annual Cybermat infestations. He also accumulates six wives over that time. Finally, he's accidentally taken by Testimony, which believes him to be an actual human, before he dies. He guilts it into letting his memories be uploaded into it, which is how an avatar appears to Twelve shortly before he regenerates.
- Ascended Extra: Started out as a supporting character in "The Husbands of River Song", getting upgraded to a companion in Series 10. While "The Return of Doctor Mysterio" was being filmed, Steven Moffat said that initially Matt Lucas had been contracted for certain episodes of Series 10, but ended up appearing in more. By the time the series came to broadcast, he was in every episode up to and including "Twice Upon a Time".
- The Atoner: "The Doctor Falls" implies he used to be a conman.
- Beware the Silly Ones: Spends most of his early appearances as Comic Relief, yet he is capable of piloting the TARDIS and was used as Mission Control when the Doctor and Bill had to navigate a Dalek spaceship in "The Pilot". In "Oxygen", he gives the Doctor a brutal What the Hell, Hero? speech when an escapade nearly gets them killed, potentially leaving the Vault and its occupant unguarded. He is then proven correct when the Doctor reveals the trip blinded him.
- Bumbling Sidekick: To River Song. The whole plot of "The Husbands of River Song" gets underway when he is sent to fetch the surgeon involved in her scheme, and instead brings back the Twelfth Doctor. Both she and the Doctor treat him haughtily, as well.
- In "The Husbands of River Song": He fetches the wrong person for River and learns of his mistake at the worst possible time. He ends up interrogated and decapitated by Hydroflax's body, his head kept alive to serve as its new head. In this state he is forced to effectively hold himself hostage so the body can interrogate Ramone. Then it takes Ramone's head too, and Nardole's head ends up "stored" within its torso, a hot and smelly place. And he almost goes down with the Harmony and Redemption when it crashes. (Not to mention that the robot short-circuiting can't be a pleasant experience.) All this in one story! When the dust has settled, however, he adjusts to his odd new existence nicely.
- In Season 10 he's constantly belittled and treated as an annoyance who's less important to the Doctor than his new companion Bill. Like others in this situation, he finds that giving as good as he gets is the best response.
- Character Development: "The Return of Doctor Mysterio" reveals that he's grown some backbone since "The Husbands of River Song" he can hold his own in snarking with the Twelfth Doctor, and he has enough insight into him to know that he's trying too hard to mask his post-River loneliness, particularly when preparing to set the villains' bomb on a course for New York City ("I know you miss her, but can't you write a poem?"). By "Oxygen", he is capable of standing up to the Doctor about as well as some of his more forthright companions.
- Cloudcuckoolander: Compared to most other companions. Other companions would've probably panicked when the Doctor, say, set a villain's bomb on a course for a city. Nardole's response (after the immediate panic) is to say that he knows that the Doctor has been through a lot, but couldn't he think of another way to express it?
- Cowardly Lion: While his fear is played for comic relief, he's willing to follow the Doctor through the increasingly insane situations the Doctor puts all his companions through. By the season finale Nardole is entirely willing to perform a Heroic Sacrifice in the Doctor's stead, though he's talked out of it.
- Cowardly Sidekick: Once he realises River's scheme is going awry because of his mistake, all he can do is hope for the best; once confronted by Hydroflax's body all he can do is plead for his life, and he's quickly rendered helpless.
- Crouching Moron, Hidden Badass: Lampshaded by Bill in "Extremis", after Nardole informs her he is the only being in all the Universe who has standing permission to kick the Doctor's arse should the need arise. Her words are, "Are you secretly a badass?" Nardole's response is that there's nothing secret about that.
- Deadpan Snarker: Can surprisingly hold his own with the Doctor during "The Return of Doctor Mysterio". He really has his moments in "The Doctor Falls", when he nonchalantly reveals that most of the surrounding farmland like windmills and bushes are highly explosive.Hazran: You think you're really something, aren't you?
Nardole: Try not to state the obvious.
- Expansion Pack Past: About Once per Episode after his initial would-be one-off appearance, he throws out some new and bizarre factoid about himself.
- Foil: He and the Twelfth Doctor have a bit of Fat and Skinny going on. Nardole is timid, anxious, unsuspecting, affable, good-mannered, and round-figured, while this particular Doctor is tall, near-bony, snarky, and grouchy with No Social Skills.
- Human Alien: Though it's not mentioned on screen pre-Series 10, according to Matt in Doctor Who Magazine #507, Nardole's not human, and is possessed of strange abilities and knowledge making him the TV series' first non-human companion (not counting Handles) since the Fifth Doctor's era. He admits that he isn't human in "The Doctor Falls", though he's close enough (after being rebuilt, at least) that a bacterium that is lethal to humans still affects him severely, and he barely survives it.
- Insistent Terminology: He makes a resounding point that he has been given full permission by the late River Song to "Kick. The Doctor's. ARSE."
- Literal-Minded: Does not understand that "restroom" and "little boy's room" are euphemisms for the same thing.
- Losing Your Head: He lost his to Hydroflax's body! He got it back by the time of "The Return Of Doctor Mysterio", though.
- Manchild: Has shades of this in his first two appearances, considering his primary outfit is a duffle coat (usually worn by small children) and he uses the term "little boy's room". It's gone entirely by Series 10.
- Mix-and-Match Man: Matt's understanding, in Doctor Who Magazine #518, is that Nardole's an alien, "with some robot replacement parts, and some human lungs".
- Morality Chain:
- River Song assigned him to be this to the Doctor before her death, knowing that he shouldn't be alone. At Missy's execution, he warned the Doctor not to go through with killing her, and subsequently did his best to hold the bored, lonesome Doctor to his vow to watch over her and the Vault.
- Interestingly, he considers the Doctor to be this to him, and worries that he'll default back to being a crook if he doesn't have the Doctor to keep him busy. Given that he used to work for River Song, it's hardly improbable that he's got a criminal past.
- Mysterious Past: We know he used to be blue at some point (thanks to a comment in "World Enough and Time") and in "Oxygen" he states that this face wasn't his original as he had to change that while on the run. Why he went on the run and changed his appearance is never made completely clear, but "The Doctor Falls" reveals he used to be involved in black market dealings. In the same episode he mentions that he doesn't actually know his origins, only that he was "found".
- Noodle Incident: His "few accidental stop-offs" during "The Return of Doctor Mysterio", including one in 12th-century Constantinople, where he claims to have accidentally become the Emperor and "ruled firmly but wisely".
- Obfuscating Stupidity: According to Steven Moffat, this is the reason for Nardole's behaviour in "The Husbands of River Song". This is likely a retcon.
- Really 700 Years Old: The Doctor's scanner in the sonic sunglasses (in "The Pyramid at the End of the World") show that he's 237 years old.
- Robotic Reveal: The opening scene of "The Pilot" strongly implies that at least part of Nardole's replacement body is robotic, as it squeaks when he moves and a bolt drops out of his sleeve when he's not carrying anything.
- Servile Snarker: Extremely. He's forced to follow the Doctor out of a sense of gratitude, but is pretty honked off at him for using the notion of rebuilding him as an excuse to have someone to talk to when everyone else is gone. And 24 years as the Doctor's toady have rendered him incapable of taking any of his crap anymore. In fact, there are a few times when he outright states a desire to kick the Doctor's arse!
- Techno Wizard: Series 10 has a few moments highlighting his computer skills, most memorably "The Doctor Falls".
- Took a Level in Badass: Somewhere between the opening of "The Return of Doctor Mysterio" and the end, he becomes a lot more intelligent and savvy, and by the time of Series 10, is more than capable of unleashing a brow-beating on the Doctor (with the occasional threat that he can and will kick his arse should the need arise).
- Unexplained Recovery: How exactly he got a new body isn't really explained, beyond the Doctor mentioning he "rebuilt" him.
- Unfazed Everyman: Nardole handles the rigors of time travel quite well, even becoming Emperor of the Byzantine Empire in the 12th century for a time during an accidental side-trip by himself. The only thing that really makes him panic is when the Doctor decides to do something particularly crazy and stupid.
- Why Did It Have to Be Snakes?: He's utterly terrified at the thought of going near Daleks.
- You Are Better Than You Think You Are: In "The Doctor Falls", the Doctor after so often belitting and ignoring him asks him an Armor-Piercing Question as they debate which one of them will stay behind to destroy the Cybermen hordes on Floor 507 and which will lead the solar farmers to safety and help protect them against future attacks which of them is stronger? The Doctor is implying that it's Nardole who will be able to handle the latter option, and Nardole realises he is right and accepts this.
Billie "Bill" Potts (Twelfth Doctor)
The principal companion of 2017, though she was first introduced with a two-minute video clip in 2016. A cafeteria worker at St. Luke's University in Bristol, she is fascinated with the lectures on time and space given by one particular, long-tenured "professor" even though she's not actually enrolled in his classes at first. The Doctor, in turn, is fascinated by her curiosity and he becomes her tutor. A crisis involving her potential girlfriend Heather leads to the Doctor having to reveal his true nature to Bill, and though he is trying to hold himself to The Promise regarding his presence at the university, he subsequently takes her on as a companion to show her the wonders she's only heard him lecture about thus far. While her relatively short tenure as a companion sees her undergo horrifying ordeals both on Earth and in the stars, the Doctor's guidance and her inner strength will bring her to a happier ending than even he can imagine is possible.
- '70s Hair: She has an afro most of the time, though it's absent in "The Lie of the Land".
- All There in the Manual: Bill's final fate is explained in the "Twice Upon a Time" novelization by Paul Cornell: After traveling the universe with Heather, the lovers returned to Earth and grew old together as humans. The relationship was so happy that Bill ultimately chose to die of old age rather than be rejuvenated again, and on her deathbed gave Heather permission to return to her immortal, traveling state. (Bill's Testimony avatar cannot explain all this to the Doctor because the Testimony gives her Laser-Guided Amnesia so she'll interact with the Doctor as she did before they were parted.)
- And the Adventure Continues: Her departure has her leaving to explore the universe further with her Living Ship and lover Heather.
- Apocalypse Maiden: Becomes this thanks to her consenting to let the Monks conquer the planet; though they don't realize it, she is the psychic conduit their Mass Hypnosis of humanity works through. Missy advises the Doctor to kill her or render her braindead to stop the Monks, and over his objections Bill is ready to make a Heroic Sacrifice to do so. However, she survives and breaks off their link, whereupon they flee.
- Armor-Piercing Question: In "Twice Upon a Time" Bill (or rather her memory avatar) asks the First Doctor why he stole a TARDIS and ran away. Her exact question impresses him:Bill: I don't mean what you ran away from. What were you running to?
1st Doctor: That's rather a good question.
Bill: Questions are kinda my thing. How are you with answers?
- Bare Your Midriff: In "Oxygen", and briefly in "The Pilot".
- Big Damn Kiss: With Heather the Pilot after she's more than Earned Her Happy Ending.
- Black and Nerdy: She's quite geeky, and likes sci-fi. She is also undoubtedly very clever, enough to sit in on and understand the Doctor's lectures despite not being a student and manages to pique his curiosity purely through her intellect. When she formally becomes a student, she very ably steps up to the Doctor's challenge of getting a first and her scores are all excellent.
- Braids of Action: Her hair is in this style in "Empress of Mars". She's a veteran companion by then, after all.
- Break the Cutie: Her experiences in "World Enough and Time"/"The Doctor Falls", as she ultimately becomes the first Mondasian Cyberman. In the end, she gets much better.
- Butch Lesbian: Downplayed, but Bill is gay, and she has a Tomboyish Name and clothing style. Her interview with the Doctor and Establishing Character Moment has her telling a story about flirting with a girl by giving her extra chips and unwittingly making her fat.
- Character Development: By the time of "The Pyramid at the End of the World", she has learned enough from the Doctor to make the kind of choice he would when she's faced with the prospect of his death: She agrees to let the Monks Take Over the World if they'll restore his lost eyesight so he can escape the lab that's about to explode, taking the line of thinking that she'll not only save him but he will be able to liberate her and her people. While she must suffer through six lonely months and a grueling Secret Test of Character in "The Lie of the Land" before she and the Doctor are reunited and he can put his plan to defeat the Monks into action, she endures and ultimately is willing to make a Heroic Sacrifice to save Earth. Luckily, she survives the process.
- Chubby Chaser: She tried to woo a girl by serving her extra chips in the canteen and, as a result, accidentally caused the girl to gain a large amount of weight. But Bill realized she liked seeing the girl bigger because she was the one who caused it.
- Constantly Curious: She's always asking questions, which amps up the teacher/student vibe that she and the Doctor have going.
- Contrasting Sequel Main Character: Coming after the closest thing he had to a soulmate, Bill is established from the outset as a lesbian (other companions have been at the most Bi the Way, including the aforementioned soulmate). Her interaction with the Doctor is that of tutor/student or surrogate parent/granddaughter, as opposed to the romance Twelve had with Clara Oswald.
- Earn Your Happy Ending: She endures incredible suffering in "World Enough and Time"/"The Doctor Falls" that puts the ordeal of the Monks to shame, including getting most of her chest vaporized, spending ten years trapped in a creepy hospital, getting betrayed by a False Friend (who turns out to be none other than the Master) and converted into a Cyberman, and watching the Doctor die, but she holds onto her sanity long enough to get rescued by Heather and ends up leaving to explore the universe with her. Meanwhile, a Testimony avatar of her is happily reunited with him shortly before his regeneration, which also lifts the burden of his guilt over not being able to undo her Cyber-conversion.
- The Everyman: As much as any companion can be. Out of the Series 10 Team TARDIS dynamic of Bill, Nardole, the Doctor and Missy she's the only one new to an adventuring life. In fact, Bill may be the most normal companion since Ten's years.
- Fridge Logic: In-Universe, when she wonders why Daleks say "Exterminate" instead of shorter words, like "Kill". Her unusual, questioning perspective on the Doctor's world is key to her character, according to Word of God.
- Gay Best Friend: She has this dynamic with the Doctor, having of course no interest in him romantically. When they talk to each other for the last time in "The Doctor Falls", she heavily implies to him that she loves him in a platonic way.
- Gender-Blender Name: "Billie", her full first name, is the feminine form of "Bill"; she typically uses the masculine form.
- Genre Savvy: She was into sci-fi and space before meeting the Doctor, and recognizes the attempt by the Doctor to erase her memories before he does it based on having previously seen it in movies.
- Imaginary Friend: Her Missing Mom becomes this once she has pictures of her. In "The Lie of the Land", she talks to her as a friend because she has no one else to turn to at the time; she knows the truth about the Monks but no one else around her does and she will be arrested for speaking up. Ultimately, her created memories of her mother and their conversations a pure fiction are what defeat the Monks in a Battle in the Center of the Mind, as they cannot rewrite fiction, only the truth.
- Missing Mom: Her biological mother died when she was young. She didn't even have any pictures of her until the Doctor went back in time to take some.
- Naïve Newcomer: She's had an ordinary life in ordinary modern day England with nothing particularly extraordinary happening to her until she was attacked by a puddle, so she doesn't know a thing about Daleks and things from outer space beyond what she's seen in movies. This is why she asks a lot of questions.
- Named After Someone Famous: She and Heather are named after William Hartnell and his wife.
- Only Known by Their Nickname: Goes by "Bill" rather than "Billie".
- Parental Abandonment: She was fostered after her mother died. Her father is never mentioned, and her foster mother appears somewhat indifferent to her.
- Parental Substitute: The Doctor takes on the role as a surrogate father or grandfather, assisting in such mundane tasks as helping her move house.
- Pop-Cultured Badass: Even in dire situations, she just can't stop referencing movies she loves.
- Preserve Your Gays: While she was turned into a Mondasian Cyberman in "World Enough and Time", she is assimilated by the Heather creature and they travel the universe together by the end of "The Doctor Falls". They even have an onscreen Big Damn Kiss after both have "died". However, she doesn't regain her human form. She's basically like Heather by that point, although she could turn back into a human if she wanted.
- Running Gag: Subverted. When meeting the Doctor for the first time, she asks "Doctor what?", rather than "Doctor who?" It also takes her a while to realize that the TARDIS is "bigger on the inside".
- Sorry, I'm Gay: A good few episodes end up with her telling potential love interests this, including the Doctor. It's inverted when members of a Roman legion actually find it rather cute that she's so restricted.
- Stepford Snarker: "Friend from the Future" suggests that she copes with life-threatening situations by cracking jokes and asking deliberately silly questions.
- Straight Man and Wise Guy: Has this dynamic with Twelve, who has to work not to crack a smile while explaining how much trouble they're in in "Friend From the Future".
- Surprisingly Happy Ending: Cyber-conversion should be Bill's death sentence since the Doctor has no means of restoring her under the circumstances, and indeed everything in "The Doctor Falls" points to a final Heroic Sacrifice, but Heather the Pilot steps in to save the day And the Adventure Continues to an extremely full life for Bill.
- Swiss Army Tears: She has these because of her connection to Heather/The Pilot. In "The Doctor Falls", they call Heather back to her and reignite the Doctor's regeneration ability. (All There in the Manual material confirms Heather was watching out for her all along.)
- Tomboyish Name: "Billie" and "Bill". She goes by the masculine latter.
- Twofer Token Minority: Black lesbian.
- Unwilling Roboticisation: Part of her Break the Cutie experience. First, she ended up with her heart being replaced by a metal one after it was vaporised by a gun blast. Then she trusted the wrong person and ended up the first full-blown Mondasian Cyberman.
- Working-Class Hero: She works in a university canteen and it's noted that Bill can't afford to attend any classes herself until the Doctor becomes her private tutor, that is.
- You Remind Me of X: It's implied her Constantly Curious nature reminds the Doctor of his granddaughter, Susan Foreman.