|Alternative name(s):||Master/Doctor, best enemies, timecock, Twissy|
|Gender category:||m/m slash, m/f het|
|Prevalence:||Temporally large, spacially moderate|
|Click here for related articles on Fanlore.|
Fandom appreciation for the possibilities of this classic enemyslash relationship dates back to at least the early 1980s. The show has historically been ambiguous about its lead character's sexuality, largely for Doylist production reasons (the adventures of an explicitly sexualized man who abducts a series of young women/men and keeps them in his 'traveling box' are not exactly the stuff of tea time telly). Due to this ambiguity, it's textually possible, and some would say rewarding, to read the show and its paracanon though a pairing-related interpretive lens. The series has gotten much less ambiguous about Time Lord romantic orientations in the 2010's, though, and in 2015 it was confirmed that gender is fluid on Gallifrey, and that gender isn't a factor for attraction. Many of the show's writers, including showrunners Russell T. Davies and Steven Moffat, are vocal fans of the Doctor/Master pairing.
A pairing involving two long-lived Time Lords is unique in that, within Doctor/Master, there are many, many other sub-pairings involving different versions of The Doctor and The Master. The Pairing Table on Livejournal community Best_enemies includes 495 different possible pairings (more than 70 of which have been written).
Novel-length fanfic can include several different iterations of the pairing, but most focus on a single pair. Due to variations in their amount of shared screen time (and arguably the attractiveness of the actors playing the characters), certain parings are more focused on by fandom than others. Ten/Simm and Twelve/Gomez are the most popular pairings, but Three/Delgado and Five/Ainley are (increasingly) not far behind.
Relationship in Canon
The Master was originally conceived as Professor Moriarty to the Doctor's Sherlock Holmes," and intended to provide the earth-bound Doctor with an ongoing archenemy/equal. Some early concept work suggested that a female Time Lord might be introduced, which has interesting implications for the later development of the Rani. Jon Pertwee (the Third Doctor) and Roger Delgado (the first Master) were personal friends, and perhaps it was their chemistry that caused their characters' on-screen interaction to escalate into a much more complicated "friendly enemies" dynamic.
Some rumours have long claimed that an early script plan would have established the Master as the Doctor's brother. The closest this ever came to being canon was a line in the fifth Doctor serial Planet of Fire, in which the Master pleaded to the Doctor, "Won't you show mercy to your own ...", before being cut off. In a gesture typical of JNT's production, it remains unclear whether he originally intended to finish this sentence with the word 'brother,' however in the New Who episode The Sound of Drums the sibling relationship is implicitly denied. Fandom has posited that given post-biological alien gender politics, one could easily complete the sentence with 'husband,' or indeed a number of more interesting nouns.
The Master was definitively introduced to Doctor Who canon in 1971, when he was played by Roger Delgado, in Terror of the Autons. The concept of a Time Lord foe had been experimented with before. One era saw the Meddling Monk, and Two Era's final serial, The War Games, introduced a Time Lord who was referred within an alien hierarchy as 'the War Chief.' The similarity of his methods and appearance to Three Era's Master have led some to retroactively dub the War Chief an early Master. The unofficial tie-in novel Time's Champion confirms this theory, though the serial's writer, Terry Nation, has downplayed it.
The Master was a frequently returning character during the third Doctor's era, and continued to return throughout the show's history. Peter Pratt and Geoffrey Beevers played a physically decayed version of the Master in Four era, until Anthony Ainley assumed the part in 1981. He remained until Doctor Who was cancelled in 1989. In 1996, the Master was played by Gordon Tipple (possibly as Anthony Ainley's Master), then by Eric Roberts in The TV movie. In the new series Derek Jacobi took the role briefly before handing over to John Simm. Aside from Pratt and Beevers (and arguably Tipple), each new actor played a different regeneration of the character, though some physical characteristics (such as goatee beards, shortness, and a propensity to wear dark colours) were carried over.
The Master returned in 2014, played by Michelle Gomez, and finally just pushed the Doctor up against a wall and snogged him into oblivion. In the next episode, the Doctor kisses her back, this time consensually.
The Master is the second-longest-established secondary character in Doctor Who fandom (after the Brigadier) and, as of New Who, he has known more regenerations of the Doctor than any other person. His relationship with the Doctor evolved as the show went on, but many factors remained constant. As well as having them regularly working together, interacting like an old married couple, and never trying very hard to truly defeat each other, the show included deliberate references to a backstory between the two. In the third Doctor serial The Sea Devils, it is established that they were in Time Lord Academy together. This childhood relationship has been widely expanded on since, both by paracanon and in the new series.
Within Doctor/Master fandom, Doctors are usually specified by number (i.e. One through Eleven) or, for AU and paracanon doctors, by nickname (Zagreus, Handy, DoctorDonna), by the canon where they appeared (Shalka!Doctor) or by actor (Lumley!Doctor, Cushing!Doctor). The Master is almost always specified by his actor (Delgado, Ainley, Roberts, Simm) with exceptions for cases where the same actor played multiple Masters (Yana, Jacobi! or Shalka), or where the same Master was played by multiple actors or no actor (such as Crispy, from the Fourth Doctor's era, or Goosnake from the TV movie). Additionally one might wish to specify a particular version of one actor's Master (Cheetah!Master from Survival, EoT!Master from The End of Time). Sometimes just the label is used alone, but primarily bang notation is used, with the label followed by simply 'Master' or 'Doctor' (written as Ainley!Master, Handy!Ten).
Stories set during the Doctor and Master's youth, while they were children in the Academy, and before they broke up the first time (if indeed they were ever together) are usually labeled Theta/Koschei. Theta Sigma or Thete is the Doctor's canonical school nickname, and the name Koschei, which fandom uses for the young Master, derives from Slavic folklore, by way of the New Adventures novels.
Master episodes: Terror of the Autons, The Mind of Evil, The Claws of Axos, Colony in Space, The Dæmons, The Sea Devils, The Time Monster, Frontier in Space
The Doctor has been exiled to Earth, following his trial in 'The War Games.' From his very first episode, 'Spearhead from Space', he begins to work for secret military operation, UNIT, as their scientific advisor. The Master is one of the returning villains from this period, and appears in every episode of series 8.
Whatever the Master's specific reasons for coming to earth (over and over again), it's clear they hinge on the Doctor. The Doctor is relatively responsive to the Master's attentions. He takes a great deal of pleasure in a battle of wits that routinely gets innocent bystanders killed. He seems to goad the Master by co-operating: playing his games right back and sending ambivalent signals. This prompts the Master to keep coming back to try his luck again when the Doctor denies him. How aware the Doctor is of his own behavior and its consequences is a bit of a mystery. Maybe he's bored, lonely, and terrible at properly telling the Master 'no'?
The Doctor's balder rejection in Colony in Space ushers in a change in their relationship: for the first time it begins to seem like the Master means a few of his death threats, or is at least angry enough with this particular regeneration of the Doctor to try to kill him in earnest.
They work together well: they have a habit of slipping into admiring each other/cooing over their random scientific projects/discoveries, as if they briefly forget they're nominally trying to kill each other. They complement each other (e.g. the Doctor riding confidently over the Master's neurotic worrying in The Mind of Evil, or the Master coming up with all the plans he inevitably ropes the Doctor into assisting him with).
They function as equals, inverses and mirrors for each other, with uncanny similarities in how they think and a deep, rational moral divide in how they perceive the world. Delgado's Master is arguably sociopathic, but he's rarely insane in the way his later incarnations can be, coming off as more amoral than immoral. The Master's bottom line is that he'd like to rule the universe jointly with the Doctor. The Doctor doesn't seem to have as clear a motivating purpose, especially as regards the Master, but he certainly can't countenance accepting the Master's offer.
Master episodes: The Deadly Assassin, The Keeper of Traken, Logopolis
Four is one of the few Doctors who seems to actively dislike the Master. Partly this is due to Four’s reduced emotional intelligence, but mostly it is the result of the production team redesigning the character of the Master, turning him from the suave, likeable figure of Delgado!Master into the being fondly known in fandom as Crispy!Master. Crispy!Master (who is now beyond his final regeneration and desperate to live) is a much more successful villain as a result of these changes. Now without his wit and charm, a literal shell of his former self, he lives only in the hope of restoring himself and is more dangerous as a result. There is no affection in the exchanges between the two, no fond remembrances of times passed on Gallifrey (which is a shame, because they’re actually there in The Deadly Assassin. Runcible would have been classmates with both of them, and Borusa probably taught the Master as well).
Their relationship (or lack of it) is much the same in Keeper of Traken, however, the dynamic shifts dramatically, once the Master manages to rejuvenate himself by stealing the body of Tremas (the father of the Doctor’s future companion, Nyssa). Much like Roger Delgado and Jon Pertwee, Anthony Ainley and Tom Baker were old friends, and they have the same physical closeness. Additionally, the Master has once again changed – regaining much of his old charms. Ainley!Master is no longer obsessed with life (he has it again), and is a much more amusing and engaging character than Crispy. Although the Doctor begins the serial Logopolis distrustful and annoyed with the Master (though perhaps less than he should be, given the circumstances), they’re soon bickering and working together happily to avoid the total destruction of the universe.
Unfortunately what could have been an interesting partnership ends before it can really begin, as the Master engineers the Doctor’s fall from a radio mast. It says something about the Doctor’s powers of forgiveness that he never seems to hold this much against the Master. It is also worth noting that although the Master claims to have spent his entire life attempting to kill the Doctor, this is the only time he manages it, and then partly by accident.
Master episodes: Castrovalva, Time-Flight, The King's Demons, The Five Doctors, Planet of Fire, Caves of Androzani
The Doctor and the Master regenerate in close proximity to each other and right after each other. They still have good bantering chemistry and a great degree of compatibility, but with additional emotional and (arguable sexual) tension between the two. Ainley's Master is far more physically domineering than Delgado's, and he leers, purrs, insinuates and stands too close to Peter Davison's rather nervous Doctor.
They still care about each other, but it's complicated by the Doctor's understanding that the Master destroyed a good chunk of the universe upon assuming this new body (in Logopolis), that he's willing to kill to get the Doctor's attention and not shy about involving others in his little gestures of affection, and that he himself came to be because the Master killed his last regeneration. The Doctor's capable of making desperate efforts to save his life in King's Demons, yet also (in the same episode) of letting him be harmed because he can't justify to himself exchanging the Master's safety for the life of an innocent. In his penultimate serial, Planet of Fire, Five decides not to save the Master's life (although unknown to him at this time, the Master does survive, ready to reappear without explanation in Six's Mark of the Rani).
The Master in this somewhat-madder-than-last-time incarnation veers from besotted (unable to countenance the idea of the Doctor's death in The Five Doctors) to homicidal. But through it all is a trust that the Doctor isn't actually capable of letting him die (to the extent that he taunts the Doctor to do it with the Master's own weapon in King's Demons, knowing full well the Doctor can't. It is significant that the Master's supposed death in Planet of Fire is a result of the Doctor's inaction, rather than his action).
Master episodes: Mark of the Rani, Trial of a Time Lord: The Ultimate Foe
The Doctor encounters the Master only twice in his very short run. In Mark of the Rani, they run into an old school ‘friend,’ the Rani, who could not be less interested in the Master’s obsessive preoccupation with the Doctor, or in the Doctor’s own need to bicker with the Master. The Doctor then encounters the Master while on trial for his life at the hands of the Valeyard, an evil version of himself. The Master intervenes on his current Doctor’s behalf, which is interesting because Delgado!Master was so interested in the possibility of a Doctor who shared his moral vision of the universe. The Master has had previous contact with the Valeyard, and is the one to explain his true nature. The Master claims he’s intervening to save the Doctor’s life not because he doesn’t want to see the Doctor dead, but because he cannot countenance a rival.
While Six may appear to actively dislike the Master (shouting criticism whenever he gets a chance), this should be understood in context i.e. he criticises Peri, his companion.
Master episodes: Survival, The TV Movie
Survival, the only Seven era story to feature the Master finds him trapped on a primitive planet sans TARDIS, and infected with the cheetah virus. His mind is fogged by the disease and increasingly primitive. He lures the Doctor to the planet in order to save himself, and then makes many remarks about animal urges. By the end of the serial, the Master's fixation with the Doctor has become an urge to hunt him. They fight an unusually physical battle as the dying world rips apart underneath them.
Seven and the Master also interact in the The TV Movie (see Eight Era). Inexplicably, this movie begins with the Daleks executing the Master for “his evil crimes”. His final request is for the Doctor to carry his ashes back to Gallifrey. At this point, the Master somehow becomes a gelatinous snake (known affectionately in fandom as Goosnake!Master), and sabotages the Doctor’s TARDIS in flight, an action that leads (indirectly) to Seven’s death.
Seven is in some ways the Doctor most like the Master. Unlike most Doctors, who are relatively impulsive, Seven plots, devising at a distance huge, game-changing schemes that only come to fruition incrementally. He’s willing to make moral decisions he shunned as a younger man. This conception of his role in the universe has much in common with the Master’s philosophy, but while Seven eliminates threats to the universe left and right, he never tries to get rid of the Master, who, despite his arguable ineffectiveness, is consistently treated as one of the series’ most formidable villains. Additionally, their admiration-shading-into-infatuation is pronounced, open and mutual in Survival.
Master episodes: The TV Movie
Following Seven’s death in The TV Movie, Eight goes on to battle the Master, who wants to ‘take his body’. At one point he screams, ‘you are my life!’ When body snatching goes poorly, the Doctor offers to save the Master, despite the Master having killed both his companions, the previous owner of his current host-body, and attempting to either co-occupy the Doctor’s body or eliminate the Doctor in the attempt. The Master refuses and falls into the Doctor’s TARDIS, and the ending leaves the question of his survival both ambiguous and problematic. Eight and Roberts!Master are "suspended between two points, wanting forgiveness and not getting it [Ainley and Five->Seven], and wanting to forgive and not being let to [Ten and Simm]. There's a potential for an equal relationship there. In the movie, Eight reaches out and tries to save him from his own actions, which I don't think he'd done since he was Three. Five always let Ainley get creamed by his own disastrous plots, and even Seven left him to die on the Cheetah planet. But Eight tried to save him."
The events of the plot leave little room for interaction between Eight and Roberts!Master, but almost imply it between Eight and whatever form of the Master still inhabits his TARDIS at the end.
If we were to take Simm!Master’s speech about the Time War in The Sound of Drums as something of an As You Know, Bob, you could posit that they knew each other then before the Master fled to the end of the universe. As to how they might get along under those circumstances, Eight has a certain Byronic sensibility that would appreciate the Master’s more ridiculous gestures, and a playful side that would work well with the Master’s strong sense of the absurd. There’s little doubt that Jacobi!Master would be interested in this Doctor, who proves in paracanon to be thoroughly charming and prone to deep attachment.
Master episodes: Utopia, Sound of Drums, The Last of the Time Lords, The End of Time (parts 1 and 2)
The Master was absent for the first two seasons of the new series, and the show's creators were evasive as to whether they had any plans to revive him. However, the Master did eventually appear in the finale of the third New Who series. His episodes made several direct references to the classic series (with vocal flashbacks to previous Masters, and the Doctor reminding the Master of “the Axons, and the Daleks”), although he was notably without a beard, either as Jacobi or Simm.
Having spent many years as a human, the Master regains his identity, immediately regenerates and steals the Doctor’s TARDIS. He then engineers his rise to Prime Minister of Britain, and subsequently ruler of the Earth in the year 2008. Between these two events the Doctor attempts to dissuade the Master from world-conquest over the phone in what is often acknowledged as the show’s slashiest scene.
The Doctor’s plan to defeat the Master and reboot the Earth necessitates a year of Martha Jones walking the Earth. During this time (generally referred to as The Year That Never Was), the Master keeps the Doctor as his prisoner. Following the Doctor’s victory, he (the Doctor) promises to “keep” the Master aboard his TARDIS, but Lucy Saxon (the Master’s “wife”: humorously referred to by the tenth Doctor as the Master’s new “beard” in the Children in Need special, Time Crash) kills the Master before this happy state of affairs can come into effect. The Doctor pleads with the Master to regenerate, but he refuses, which is (he says) a victory at last.
The Master reappears at a time in which the Doctor is convinced he is the last of the Time Lords, and it is possible his extreme interest in the Master this time round is a result of wanting to bond with another member of his species. However, given the Doctor’s general dislike of the Time Lords (as shown in previous episodes, and in the future serial The End of Time), his claiming of the Master as his responsibility may be down to more than their genetics.
In the End of Time the Master returns, and quickly develops a plan to imprint his appearance and personality onto the human race. The Doctor spends a lot of time this serial attempting to connect with the Master, and remind him that he could be as “beautiful” as he was a child, a move that arguably pays off. At the end of the serial, the Master tells him to “step out of the way” of his battle with Rassilon, saving the Doctor’s life (temporarily) and dooming himself to what may be oblivion, or at the very least the Time War he tried so hard to escape.
This ending leaves his relationship with the Doctor extremely unclear. Interestingly the decision to have the Master sacrifice his life for the Doctor's could be said to derive from a similar Three serial, The Final Game, which was discussed, but never fully scripted or filmed due to Delgado's death in an automobile accident while filming on the continent. In a way, the Master has come full-circle.
Simm!Master was designed specifically by writer Russell T. Davies to echo the tenth Doctor: he is young, bouncy, funny, and rude. Sadly they were never at their best together: the tenth Doctor is old and sad in The Last of the Time Lords, and both of them are aware they’re about to die in The End of Time. The Doctor shows more care for the Master than almost anyone else in the new series, becoming serious around him and constantly trying to appeal to his better nature. The Master meanwhile is somewhat dismissive of the Doctor this regeneration (although he seems to have some respect for the Doctor’s previous incarnations i.e. musing about the Doctor closing the rift at the Medusa Cascade), but when the Doctor collapses after being shot with lightning/the Master’s life force, the Master runs over to catch him (before dropping him, disgusted with himself). When asked about the Master’s reaction here in the online commentary for this episode, Russell T. Davies remarked, “Well, he loves him really.”
Master episodes: Deep Breath, Into The Dalek, The Caretaker, Flatline, In the Forest of the Night, Dark Water, Death in Heaven
The Master, played by Michelle Gomez, has escaped from the Time War and has returned to bother the Doctor. This incarnation of her makes no secret of her feelings for the Doctor, and calls him her "boyfriend". She conceals her identity at first, staying hidden from him for most of the season, until he finally encounters her in the middle of her base of operations. She pretends to be a droid upon seeing him and, in this persona, snogs him senseless up against a wall. The Master then pulls the Doctor's hand to her chest, making him feel her double heartbeat, but he doesn't understand (or outright refuses to register) this clue. He soon acknowledges that she's a Time Lady, and she tells the Doctor that she's "the one you abandoned [...] the one you left behind."
When she finally does reveal her identity to him, the Doctor panics, realising that the Cybermen army (made of the bodies and trapped minds of the dead) that she revealed to him earlier is completely under her command. However, said army turns out to be her gift to him, in an attempt to restore their friendship. By making the Doctor in charge of an army, she hopes that he will see that they're not so different. The Master mockingly gets down on her knees for the Doctor, waiting for his response. The moment triggers an epiphany in the Doctor -- the realisation that he may not be a good man, but he's not a bad man either, or a hero. He's just "an idiot, with a box and a screwdriver". The Doctor gets down on his knees to kiss the Master in joy, to thank her for making him realise this once again.
The Doctor's companion, Clara, attempts to kill the Master for everything she's done, but the Doctor won't let her -- he wants the burden of this murder to fall on him, not on Clara. However, before he can go through with it, the Master is disposed of by the Cyberconverted corpse of the Brigadier (see Third Doctor era), who had earlier broken out of his cyber-programming when the Master tried to murder his daughter Kate.
Naturally, although the Master seems to die, she actually teleported out and will return in series 9.
From around the 1970s, there has been a large variety of authorised (and unauthorised) paracanonical media on offer to fans. Though the Master only appeared in a few of the books and audios, several of them expanded on the Doctor and Master's historical friendship, including New Adventures novels such as Lungbarrow and the Big Finish Audio Master. For a full list of the Master's appearances in paracanonical media, see Tardis Wiki.
Significantly for Doctor/Master fandom, there were also two specials: the 1999 Red Nose Day comedy special The Curse of Fatal Death, and the 2003 animated pilot Scream of the Shalka. In Curse of Fatal Death having regenerated a number of times, a female Doctor played by Joanna Lumley ends the serial by eloping with the Master (Jonathan Pryce). In Scream of the Shalka, an alternate Ninth Doctor (Richard E. Grant) is shown living on his TARDIS with a robotic version of the Master (Derek Jacobi): Shalka writer Paul Cornell intended this relationship to be platonic and asexual, but has since come around to the shipper front and has become a vocal proponent of the romantic interpretation.
History of the pairing in fandom
Early Doctor Who fanfic
Most of pre-internet Doctor Who fandom is not currently documented online. We do know that early Doctor Who fanfic was, like a lot of scifi media fandom, largely zine based and focused on gen, but with some het and a small amount of slash. Doctor/Master was perhaps the most common slash pairing, although the Doctor was also written with various male companions. The oldest Doctor/Master fic available online as of late 2010 is "Ring of Truth", by The Android, published in Uncharted Waters #10 and Dyad #13, and the connected "Island in Time" by Julia, which was published in Uncharted Waters #1.
Before the start of the new series in 2005, most Doctor Who fanfic online was hosted at alt.drwho.creative, the connected archive The Panatropic Network (1998- 2002), and, from 2003, A Teaspoon and an Open Mind. The newsgroup and Panatropic allowed slash and adult fiction, and this included a small amount of Doctor/Master.
The most significant Doctor/Master story from this era may have been "Bitter Aloes" by Anne Ellis, a story set during the fifth Doctor era that included themes of non-con, darkfic, and bdsm. This story became embroiled in an ongoing wank in late-1990s Who fandom. As a result Panatropic established a separate Adult section, and some Doctor Who slash writers became less willing to participate publicly in the fandom.
Revitalization of the pairing
Interest in the pairing grew due to with the overall revitalization in Doctor Who fandom following the start of the 2005 series. Stories were written in previous eras, and with original-character versions of the Master paired with the new Doctors.
Many New Who fans, however, were unaware of or uninterested in Classic Who (and as an extension, the Master, who had at that point made no appearance in the new show), and the pairing did not really take off until the series three season arc, which culminated in the season finale triptych Utopia/The Sound of Drums/Last of the Time Lords. These Foe Yay and sexual-tension-laden episodes were so embraced by slash-inclined fans that the pairing's fandom was reborn almost overnight.
In the period just after The Last of the Time Lords AU stories in which the Master accepted the Doctor's suggestion to travel with him in his TARDIS proliferated. In the summer of 2007 there were probably more stories set in such AUs than in canon-based universes (though the cheese-cloth permeability of Canonicity in a show based on time travel and the malleability of events and histories means the barrier between 'normal' and AU fic is stretched exceptionally thin in the Whoniverse). These are sometimes called "Alternate Season 4" stories, partly due to ariastar's novel-length Doctor/Master AU, which was posted in an lj called dwseason4. Wiccanslyr established the livejournal community slash_lords, which focused on Doctor/Master, on July 4 2007--less than a week after the last of the Series Three episodes aired. Fic set during the Year That Never Was was also extremely common, and became known as 'Valiant!fic', after the Master's airship. Although the Doctor was shown to be old at the beginning and end of the year, most people writing in this sub-genre assumed the Master de-aged the Doctor whenever convenient.
During this period, many people who were unfamiliar with Old Who and previous Masters entered the fandom. Stories set during the tenth Doctor's era heavily dominated the internet community. However, an increasingly vocal contingent in the fandom were enthusiastic about the Doctor and the Master as they appeared in previous eras, and New Who fans, eager to consume more information about their new pairing, began watching the older episodes. In February 2008 the livejournal community Best_enemies was founded by x_los, with goals such as being "more of a community than a ficdump/artdump" and encouraging more "classic!slash". Best_Enemies continues to be a community gathering place, with regular challenges and discussion posts, an ongoing anon fic meme, an auxiliary RPG, active chatrooms, and many various other activities. In March 2008, Versaphile founded the Prydonian, a fanfic archive for Doctor/Master.
During the next several years, fanworks of various kinds continue to be steadily produced, with bursts of increased activity around the airing of subsequent episodes. The Master's appearance in the 2009 special The End of Time also generated interest and increased participation in the fandom, but to a much lesser extent than after The Sound of Drums/The Last of the Time Lords. In September 2010 the community doctor_and_master was founded on Dreamwidth by evilawyer to provide a community for Doctor/Master fans seeking a place off livejournal.
Fanon and Fanfic Tropes
Many Doctor/Master fans, and their fanfics, assume that the Doctor and Master were in a relationship before the show began. Some even posit that they were married (see above), and/or that Susan is a result of a shared relationship. It is generally assumed they broke up while still at the Academy, or just afterwards, probably as a result of something objectionable the Master did or the Doctor's own restlessness.
There is a general acceptance of the idea that necks are an erogenous zone for Time Lords. This belief is due partly to the large collars the non-renegades wear on Gallifrey (and the tendency even of the renegades to cover their necks), and a scene in one of the the EDAs, in which the Doctor responds very appreciatively to a back massage. If this is true, then the phone-cord strangulation of the Doctor in Terror of the Autons takes on new erotic significance.
As the pairing includes two supposed enemies, one of whom is a known villain, it is perhaps not surprising that one of the most prevalent tropes in the D/M fandom is darkfic. Both physical and emotional violence are inflicted on one or other of the participants (generally the Doctor), including bdsm, dubcon (sometimes noncon), forced regeneration, and general humiliation. This trope is particularly common in new who fanfic, due to the way the pairing was represented in canon (Simm is the first Master to physically strike the Doctor, he sexually harasses his wife and other staff members, and keeps the Doctor in a dog house/bird cage. The Doctor is still desperate for his affections, and cries over his corpse), though it also applies to Classic fanfic.
The softer (or schmoopier) side of Doctor/Master is, conversely, represented chiefly in Classic Who fanfic and art. Surprisingly, fluffy fics in which the protagonists leave off saving the world and arguing to have tea or sex are not un-common. Admittedly, many of these fics are AUs, in which the Doctor and the Master develop some form of compromise, but not all. In a non-AU fic it is possible that they make love after (or occasionally while) working together to save the world, but in this case under the proviso (typically from the Doctor's side) that such a reprise is temporary. It should be noted that even in the fluffiest fics, there is usually still an undercurrent of bickering and one-upmanship. Classic fic is more likely to depict the Master as the more romantically invested partner, which perhaps explains why fluffy fics are more common in Classic Who (i.e. the Master is more likely to adapt to a way of life the Doctor finds acceptable).
Crack or humorous fic and art are relatively common, possibly due to the comedic tension between the Master as a villain and the Master as a romantic partner.
Academy era fic typically picks and chooses from the somewhat uneven and contradictory canon established by the books and audios. Usually Theta and Koschei are roommates, and potentially troublemakers. Ushas (the NA school nickname for the Rani) often features, and the Doctor's paracanonical brother, Braxiatel has been known to put in an appearance.
Crossovers with the TV show Life on Mars in which John Simm's character Sam Tyler is a fobwatched version of his Master were extremely common just after the airing of Last of the Time Lords (a couple of months after the LoM finale).
Time and the Gallifreyan language are often used as erotic tools, the latter particularly prevalent in Ten/Simm fic - at which point, the language is one that only they know.
A very incomplete list of some of the best known fics in the fandom.
- Sartorial Differences by aralias
- Eight/Master (including Goosnake, Roberts, Jacobi)
- Living Things by bagheera_san
- A Teaspoon and an Open Mind (link) (general DW archive)
- The Prydonian (D/M archive)
- Fanworks tagged The Doctor/The Master at AO3
- Best_enemies (D/M livejournal community)
- Slash Lords (D/M livejournal community)
- Doctor_and_Master (D/M Dreamwidth community)
- DW_Slash (general DW slash livejournal community)
- Scream of the Shalka webcast (free to watch!)
- Big Finish Audios
- The Doctor Who Reference Guide
- Doctor Who Wiki
- Rassilon, Omega and that Other guy (extensive notes on Gallifrey and its people)
- Time Lord biology (all you have ever wanted to know on the subject)
- Commentary on 'Any Time at All', fic and commentary by reasonabsurd.