Nor, ultimately, was it ever explicitly made clear what had caused the Doctor to leave his people, although it is suggested in some stories that he was an involuntary exile and in others that he had simply grown tired of the restrictions of Time Lord society and left.
The Time Lords are normally considered one of the oldest and most technologically powerful races in the Doctor Who universe. The small number of beings more powerful than the Time Lords includes the (now extinct) Osirans and higher powers of the universe such as the Black and White Guardians and, from the spin-off novels, which are of uncertain canonicity, The People, with whom the Time Lords signed a non-aggression treaty. The power of the Time Lords appears limited by their policy of non-interference with the universe and sometimes by intense internecine division.
However, the view that they are, to a degree, custodians of time developed in the spin-off media. This is also suggested in the television series; in The War Games the Time Lords return time-displaced humans abducted by the War Lord to their proper time zones on Earth. The name of the Time Lords' central hall, the Panopticon, suggests that they are perpetual observers of all existence.
In "Father's Day the Ninth Doctor remarks that prior to their destruction, the Time Lords would have prevented or repaired paradoxes such as that which attracted the Reapers to 1987 Earth. In "Rise of the Cybermen", the Tenth Doctor mentions that while the Time Lords were around, travel between alternative realities was easier, but with their demise, the paths between worlds were closed. In "The Satan Pit", the Tenth Doctor states that his people "practically invented black holes. Well, in fact they did."
Time Lords appear human, but differ from them in many respects. All Time Lords in the classic television series were portrayed by white adults, although in Planet of the Spiders some of those white actors used yellowface to appear Tibetan. A black Time Lord appears in the 2007 episode "The Sound of Drums" and others in the spin-off novel The Shadows of Avalon and the comic strip Blood Invocation, both by Paul Cornell. In addition, Time Lord founder Rassilon was portrayed in several audio plays by black actor Don Warrington, and a black Time Lord was seen in various crowd scenes in 1975's The Deadly Assassin. An 8-year-old Gallifreyan child (implied to be the renegade Time Lord known as the Master) was depicted in "The Sound of Drums" and appeared identical to a human child of the same age.
No explanation is given in the series as to why Time Lords look human, nor why the universe seems filled with predominantly humanoid species. The Virgin New Adventures novel Lucifer Rising by Andy Lane and Jim Mortimore suggests that the Time Lords were the first sentient life-form. As such, their evolutionary pattern created a morphogenetic field that resonated across the universe, making the development of humanoids far more likely. The Big Finish Productions audio play Zagreus offers a more sinister explanation, that the xenophobic Rassilon seeded the universe with biogenic molecules so that (save for worlds where humanoids could never evolve) only intelligent species that approximated the Gallifreyan humanoid norm would develop. However, in the Cushing movie Dr. Who and the Daleks (though not necessarily thought to be canon), one of the Thals states that the 'humanoid' form has been proven to be ideal for survival, hence many species in the universe are humanoid. The canonicity of these accounts, as with all spin-off media, is unclear.
Time Lords are extremely long-lived, routinely counting their ages in terms of centuries. It is not known how long a Time Lord can live, although the Doctor claimed in The War Games that Time Lords could live "practically forever, barring accidents." In The Daleks' Master Plan the First Doctor is able to resist the effects of the Time Destructor better than his companions, who are visibly aged by it; one of them, Sara Kingdom, ages to dust before the Destructor device can be reversed, although the Fourth Doctor is briefly aged 500 years in The Leisure Hive, which leaves him an old man but still somewhat active. A similar situation occurred in "The Sound of Drums", where the Master uses specially made technology to age the Tenth Doctor by a century, leaving him in a frail and helpless state. A further application of this in "Last of the Time Lords" ages the Doctor another 900 years and turns him into a shrunken, wrinkled humanoid. It is unclear if this effect is the result of later regenerations not being as long lived or the artificial manner of ageing, given the first incarnation of the Doctor was still quite active at 450 when he regenerated.
The Doctor is quoted as saying 'I don't age' in the episode ("School Reunion") when talking to his companion, Rose, although in this he may have been referring to the results of regeneration rather than immunity to the ageing process. His statement is otherwise contradicted by the First Doctor's claims to be "wearing a bit thin" and encounters between different regenerations where the previous actors have necessarily aged noticeably (The Two Doctors, "Time Crash").
The series has occasionally suggested that Time Lords have a different concept of ageing to humans. In Pyramids of Mars, the Doctor considers an age of 750 years to be "middle-aged". In "The Stolen Earth", he refers to being a "kid" at 90 years old.
It is implied (in The Invasion of Time and The Deadly Assassin) that the terms "Gallifreyan" and "Time Lord" may not be synonymous, and that Time Lords are simply that subset of Gallifreyans who have achieved the status of Time Lord via achievement in the Gallifreyan collegiate system; in the episode "The Sound of Drums" The Doctor talks of 'children of Gallifrey' which implies that children are Gallifreyan before they are Time Lords. Romana and the Doctor have also referred to "Time Tots", or infant Time Lords, and (in "Smith and Jones") the Doctor refers his compatriots and he playing "with Röntgen bricks in the nursery". In "The Sound of Drums", the Master is seen as a child, apparently at the age of 8.
Other physiological differences from humans include two hearts (which normally beat at 170 beats a minute), an internal body temperature of 15 degrees Celsius and a "respiratory bypass system" that allows them to survive strangulation. Time Lords can also survive full exposure to the vacuum of space with no ill effects, though in such cases, even with their respiratory bypass boosting the length of time they can go without air, when in vacuum for an extended period a Time Lord must take a supply of air along, or else suffocate. A commonly held piece of fan continuity is that Time Lords only grow their second heart during their first regeneration, though in "The Shakespeare Code" one of the Tenth Doctor's hearts is stopped and he wonders aloud how humans can cope, and in "The Doctor's Daughter", Jenny is shown to have two hearts. If severely injured, Time Lords can go into a healing coma which lowers their body temperature to below freezing. In the serial Destiny of the Daleks, Romana was able to voluntarily stop both of her hearts beating, to fool the Daleks into believing that she was dead. In "World War Three", the Doctor is able to shake off an electrocution attempt which is fatal to a number of humans, and appears unaffected by the energy whip wielded by the Sycorax in "The Christmas Invasion". In cases of non-fatal injury, Time Lords who have recently regenerated can use left over cellular energy to heal and even regrow severed limbs, as seen in The Christmas Invasion where the Tenth Doctor regrows a hand and in The Doctor's Daughter where Jenny heals from a gun shot wound (although in her case she was recently "born" and the shock of the wound did throw her into a near coma, only reviving later on.). Also seen in Journey's End (Doctor Who), is the apparent ability to siphon off regeneration energy in order to cancel the effect of changing appearance; which requires them to have a "matching receptacle" (in this case the Doctor's severed hand), which is usually impractical. It remains to be seen whether this technique counts as regenerating fully, and thus losing one of the Time Lord's inherit 12 regeneration allotment.
Time Lords, or at least the Doctor, can read extremely quickly. They appear to have greater physical stamina than humans and need considerably less sleep. In "Smith and Jones" the Tenth Doctor says that Röntgen radiation poses no real threat to Time Lords, and proceeds to absorb an amount that would be lethal to a human, which he subsequently expels through his foot. The Doctor also shows a greater tolerance to cold compared to humans in Planet of the Ood and even Romana in The Ribos Operation
The Doctor states in The Mind of Evil that a pill (apparently aspirin) could kill him. It is not known whether this is a susceptibility shared by all Time Lords, or merely something like an allergy unique to the Doctor (or if he was lying for comedic effect).
The biological imprint (also known as bio-data) of a Time Lord, which also defines his personal history, is kept in the Matrix, a computer network that contains the sum total of all Time Lord knowledge. The unauthorised extraction of a Time Lord's bio-data is tantamount to treason.
It is stated that the Time Lords are biologically suited for time travel. Also in The Two Doctors, the Doctor states that the "Rassilon Imprimatur" allows Time Lords to safely travel through time, becoming symbionts with their TARDISes, and that the reason other species are incapable of developing time travel are that they lack the imprimatur. (However, he implies later that he was lying about some or all of this information to mislead the Sontarans.) At the beginning of The Trial of a Time Lord, the Doctor suggests that a number of elder Time Lords were able to use their combined mental energy to summon his TARDIS against his will.
It is stated and seen in the Fourth Doctor serial The Robots of Death that Time Lords are immune to the voice-changing effects of helium. However, the Doctor alludes to this being a learnt ability rather than a basic biological immunity.
In "The Unicorn and the Wasp", the Tenth Doctor is able to overcome the effects of cyanide by "stimulating the inhibited enzymes into reversal". This is done by consuming ginger beer, protein (from walnuts) and salt (from anchovies, as pure salt is "too salty"). Finally a shock - which is given in the form of a kiss from Donna - triggers the 'detox' effect.
In "The Girl in the Fireplace", the Tenth Doctor reads the mind of Madame de Pompadour--and in the process, to his surprise, she is able to read his mind as well. In Paul Cornell's Virgin New Adventures novel Love and War, the Doctor uses a similar method to read the mind of his companion Bernice Summerfield. He later displays his telepathic communion powers in "Fear Her" and in "The Shakespeare Code", where by using his mind melding technique he is partially able to relieve a man of his mental illness as he traces back through his memories. In "Planet of the Ood", he seems able to temporarily confer some degree of telepathy on his companion Donna Noble, so that she can hear the telepathic song of the Ood. When she is unable to bear the song, the Doctor removes the ability. It is unclear at this point whether the Doctor is actually able to gift another being with telepathy, if he simply switches on or off telepathic potential that those beings already possess, or if he just shares his thoughts with them telepathically.
The Doctor also contacts the Time Lords by going into a trance and creating an assembling box (suggesting telekinesis as well) in The War Games. In The Two Doctors, the Doctor engages in astral projection, but warns that if he is disturbed while doing so, his mind could become severed from his body and he could die. In "Last of the Time Lords", the Doctor telepathically interfaces with a network tapped into the human population who collectively chant his name. The focus of psychic energy granted the Doctor the ability to de-age himself, float through the air, deflect shots from the Master's laser screwdriver, and telekinetically disarm the Master while surrounded in a powerful blue glow.
In addition, it is implied that Time Lords may be clairvoyant, or have additional time-related senses. In The Time Monster and Invasion of the Dinosaurs the Third Doctor is able to resist fields of slow time, being able to move through them even though others are paralysed. In City of Death both the Fourth Doctor and Romana notice distortions and jumps in time that no one else does. In the 2005 series, the Ninth Doctor claims that he can sense the movement of the Earth through space as well as being able to perceive the past and all possible futures. He is also able to concentrate and time his motions well enough to step safely through the blades of a rapidly spinning fan and later claims that if any Time Lords still existed, he would be able to sense them. As the Tenth Doctor he repeats this assertion, adding also that he is somehow innately able to sense which events in time are 'fixed' and which are in 'flux'. In the original series episode Warrior's Gate, Romana is called a 'time-sensitive' by a marauding slaver and, though she seems to deny this, is able to interface with his spaceship in ways that only a 'time-sensitive' is supposed to be able to. In "Utopia" the Doctor states that he finds it difficult to look at Captain Jack Harkness because Jack's existence has become fixed in time and space. The Tenth Doctor also mentions to Donna Noble, in the episode The Fires of Pompeii, that Time Lords can see the past, presents, and all possible futures (as the Ninth Doctor told Rose Tyler in The Parting of the Ways). This also implies, because he is the last of the Time Lords, that the burden is much more difficult to bear.
In the Series 4 episode "Journey's End", the Tenth Doctor was shown to use his telepathic abilities to wipe Donna Noble's mind of certain memories, specifically the memories of her travels in the TARDIS. The War Games showed that other Time Lords are also able to erase people's memories, as in that story, Jamie and Zoe's travels with the Doctor were erased from their memory, and the council of Time Lords also put a memory block on the Doctor so he could not pilot the TARDIS.
Time Lords also have the ability to regenerate their bodies when their current body is mortally wounded. This process results in their body undergoing a transformation, gaining a new physical form.
Regenerations can be traumatic events. In Castrovalva, the Doctor requires the use of a Zero Room, a chamber shielded from the outside universe that provides an area of calm for him to recuperate. He comments that there is an excellent polygonal zero room beneath the junior senate block on Gallifrey. The Time Lord's personality also sometimes goes through a period of instability following a regeneration.
It was first stated in The Deadly Assassin that a Time Lord can regenerate twelve times before dying (thirteen incarnations in all). There were exceptions to this rule, however: when the Master reached the end of his regenerative cycle, he took possession of the body of another person to continue living. The Master was also offered a new cycle of regenerations by the High Council to save the Doctor from the Death Zone, which may indicate that there are methods to circumvent the 12 regeneration limit. The Master says in "The Sound of Drums" that the Time Lords "resurrected" him to fight in the Time War, which appears to support this. It was revealed in "The Brain of Morbius" that the Time Lords also use the Elixir of Life in extreme cases, where regeneration is not possible. This may be the reason for additional regeneration cycles being granted.
Also in The Deadly Assassin, several Time Lords including the President are stated to have been "murdered" and are not stated to have regenerated. Although it is possible that all of the Time Lords killed were at the end of their regeneration cycles (somewhat more likely with a retiring President: potentially his reaching the end of his regeneration cycle was the very reason for his retirement), it is also possible that regeneration regardless of how many regenerations the individual Time Lord has already undergone is a conditional and non-inevitable phenomenon. In The Deadly Assassin at least one of the murders was carried out with a 'staser', possibly a weapon designed to both kill and prevent regeneration (stasers are also stated to have little effect on non-living tissue). Some victims, such as Runcible, were possibly "just Gallifreyans" and not Time Lords (see above), and so may not have had the ability to regenerate.
In Destiny of the Daleks, Romana showed the ability to rapidly change form several times in a row during her first regeneration and apparently had the ability to change into whatever appearance she desired. This brings up many questions about the degree of control that Time Lords have over their regeneration process. It should be noted, however, that, despite showing several appearances, Romana regenerated only once on that occasion.
Whether or not Time Lords can recognise each other across regenerations is not made entirely clear in the original television series. In The Deadly Assassin an old classmate recognizes the 4th Doctor despite his changes in appearance. And in a later serial, The Armageddon Factor, another alumnus immediately recognises the Doctor, though the Doctor does not recognise him. In Planet of the Spiders, the Third Doctor has trouble recognising his former mentor. In The Five Doctors, the Third Doctor is also unable to initially recognise the Master in his non-Gallifreyan body. Similarly, the Eighth Doctor is unable to recognise the Master while he possesses a human body in the 1996 television movie. The Master recognises the Seventh Doctor on sight in Survival, although this may simply point to an earlier, unseen encounter.
The Tenth Doctor does not recognise the human form of the Master in "Utopia", although the Doctor did recognise him, and name him "Master", as soon as he recovered his Time Lord physiology and mind. Also in Utopia, the Master, just before regeneration, claims that he shall regenerate into a younger body, implying that a Time Lord can even choose the form of their new body. In "The Sound of Drums" the Doctor states that Time Lords can "always" recognise each other, although, while on Earth, the Master used satellites with a telepathic network to mask his presence from the Doctor. However, in "Time Crash," the Fifth Doctor could not instinctively recognise that the Tenth Doctor was a Time Lord, nor did he guess that they were different incarnations of the same Time Lord.
In "The Last of the Time Lords", when the Master is fatally wounded, he chooses not to regenerate, essentially committing suicide rather than regenerate and be kept prisoner by the Doctor forever. This again implies that regeneration is not inevitable and can indeed be refused.
In "Turn Left", the Tenth Doctor is killed "too quickly for him to regenerate" in an alternate history where he is killed in his own rampage against the Racnoss without Donna to stop him and ultimately save his life. This death was presumably caused by flooding of the building, which the Doctor was aware of, and would not have happened any more suddenly than the Sixth Doctor's apparent death by trauma in Time and the Rani (although spin-off media have suggested that the assault on the TARDIS was not the sole reason for the Doctor's death).
In general, the Time Lords are an aloof people, with a society full of pomp and ceremony. The Doctor has observed that his people "enjoy making speeches" and have an "infinite capacity for pretension". The Time Lord penchant for ceremony extends to their technology, with various artefacts given weighty names like the Hand of Omega, the Eye of Harmony or the Key of Rassilon.
The Doctor has also characterised the Time Lords as a stagnant and corrupt society, a state caused by ten million years of absolute power. Brother Lassar, in the episode "School Reunion", describes the Time Lords as "a pompous race" of "ancient, dusty senators... frightened of change and chaos" and "peaceful to the point of indolence". Their portrayal in the series is reminiscent of academics living in ivory towers, unconcerned with external affairs. The Doctor states that the Time Lords were sworn never to interfere, only to watch ("The Sound of Drums"). It has been suggested that, since perfecting the science of time travel, they have withdrawn, bound by the moral complexity of interfering in the natural flow of history (compare with the Prime Directive from Star Trek); in Earthshock, the Cyberleader, when notified of the arrival of a TARDIS, is surprised at the presence of a Time Lord, stating "they are forbidden to interfere." In The Two Doctors, it is suggested that Time Lords are responsible for maintaining a general balance of power between the races of the Universe.
While interference is apparently against Time Lord policy, there are occasions when they do intervene, albeit indirectly. The Time Lords occasionally send the Doctor on missions that required plausible deniability, as in The Two Doctors, and sometimes against his will, like in Colony in Space and The Monster of Peladon. He is also sent on a mission in The Mutants which was intended to help preserve the existence of a unique race, which was being destroyed by the excesses of the Earth empire. The Doctor's mission in Genesis of the Daleks even involves changing history to avert the creation of the Daleks, or at least temper their aggressiveness.
Children of Gallifrey are taken from their families at the age of 8 and admitted into the Academy. Novices are then taken to an initiation ceremony before the Untempered Schism, a gap in the fabric of reality that looks into the time vortex. Of those that stare into it, some are inspired, some run away and others go mad. The Doctor suggests that the Master went mad, while admitting that he ran away.
Each Time Lord belongs to one of a number of various colleges or chapters, such as the Patrexes, Arcalian, and the Prydonian chapters, which have ceremonial and possibly political significance. In The Deadly Assassin, it is explained that each chapter has its own colours; the Prydonians wear scarlet and orange, the Arcalians wear green, and the Patrexeans wear heliotrope. However, in that same serial, Cardinal Borusa, described as "the leader of the Prydonian chapter" wears heliotrope. Other Prydonians wear orange headdresses with orange-brown (not scarlet) robes. Others chapters mentioned in spin-off novels include the Dromeian and Cerulean chapters. The Prydonian chapter has a reputation for being devious, and tends to produce renegades; the Doctor, the Master and the Rani are all Prydonians. The colleges of the Academy are led by the Cardinals. Ushers, who provide security and assistance at official Time Lord functions, may belong to any chapter, and wear all-gold uniforms.
The executive political leadership is split between the Lord President, who keeps the ceremonial relics of the Time Lords, and the Chancellor, who appears to be the administrative leader of the Cardinals and who acts as a check on the power of the Lord President. The President is an elected position and on Presidential Resignation Day, the outgoing President usually names his successor, who is then also usually confirmed in a non-contested "election". However, it is still constitutionally possible for another candidate to put themselves forward for the post, as the Doctor did in The Deadly Assassin. In that story, the Presidency was described as a largely ceremonial role, but in The Invasion of Time the orders of the office were to be obeyed without question.
The President and Chancellor also sit on the Time Lord High Council, akin to a legislative body, composed variously of Councillors and more senior Cardinals. Also on the High Council is the Castellan of the Chancellory Guard, in charge of the security of the Citadel, whom the Doctor has referred to as the leader of a trumped-up palace guard. According to the constitution, if while in emergency session the other members of the High Council are in unanimous agreement, even the President's orders can be overruled.
TARDISes are characterised not just by their ability to travel in time, but also their dimensionally transcendent nature. A TARDIS's interior spaces exist in a different dimension from its exterior, which is how it's bigger on the inside. The Doctor states that transdimensional engineering was a key Time Lord discovery in The Robots of Death. In the revived series, the TARDIS has an organic look, and the Doctor states in "The Impossible Planet" that TARDISes are grown, not made.
Fitting their generally defensive nature, Time Lord weapons technology is rarely seen, other than the staser hand weapons used by the Guard within the Capitol. Stasers (acronym unknown) are lethal energy weapons, specifically designed to prevent the unwanted regeneration of rogue Time Lords; staser beams also shatter the crystalline structure of non-organic targets.
Standard TARDISes do not generally seem to use any on-board weaponry, although War or Battle TARDISes (armed with "time torpedoes" that freeze their target in time) have appeared in the spin-off media. In the novels, the Eighth Doctor's companion Compassion, a living TARDIS, has enough firepower to annihilate other TARDISes.
One exception to the Time Lords' defensive weaponry is the de-mat gun (or dematerialisation gun). The de-mat gun is a weapon of mass destruction that removes its target from space-time altogether, as seen in The Invasion of Time. The de-mat gun was created in Rassilon's time and is a closely guarded secret; the knowledge to create one is kept in the Matrix and is available only to the President. To make sure this knowledge is not abused, the only way to arm a de-mat gun is by means of the Great Key of Rassilon, whose location is only known to the Chancellor. As a means of extreme sanction, the Time Lords have also been known to place whole planets into time-loops, isolating them from the universe in one repeating moment of time as well as hurling planets from one galaxy to another using a weapon referred only as a magnetron in the episode Trial of a Time Lord.
In the Eighth Doctor Adventures novel The Ancestor Cell by Peter Anghelides and Stephen Cole, the Time Lords are shown to house other weapons of mass destruction in a stable time eddy known as the Slaughterhouse. In the Doctor Who Annual 2006, a section by Russell T Davies says that during the Time War, the Time Lords used Bowships (used against the Great Vampires in an ancient war), Black Hole Carriers and N-Forms (war machines first mentioned in the Virgin New Adventures novel Damaged Goods, written by Davies).
Details of the Time Lords' history within the show are sketchy and are, as is usual for Doctor Who continuity, fraught with supposition and contradiction. The Time Lords became the masters of time travel when one of their number, the scientist Omega created an energy source to power their experiments in time. To this end, Omega used a stellar manipulation device, the Hand of Omega, to rework a nearby star into a new form to serve that source. Unfortunately, the star flared, first into a supernova, and then collapsed into a black hole. Omega was thought killed in that explosion but unknown to everyone, had somehow survived in an antimatter universe beyond the black hole's singularity. Rassilon, the ultimate founder of Time Lord society, then took a singularity (assumed by fans and the spin-off media to be the same one as Omega's) and placed it beneath the Time Lords' citadel on Gallifrey. This perfectly balanced Eye of Harmony then served as the power source for their civilisation as well as their time machines. In "The Satan Pit", the Doctor states that his race "practically invented black holes. In fact, we did", presumably a reference to the singularity created by Omega.
At some point in their history the Time Lords interacted with the civilisation of the planet Minyos, giving them advanced technology. This met with disastrous results, the Minyans destroying themselves in a series of nuclear wars (Underworld).
As of the current series, the Time Lords have, according to the Doctor, all perished at the conclusion of a Time War with the Daleks, leaving the Doctor the sole survivor and the last of his race (It was also revealed that the Doctor was responsible for the extinction of both races, as was confirmed by the Beast). This may not be entirely true however. In the episode "Gridlock", the Face of Boe tells the Doctor with his dying breath that the Doctor is "not alone".
In the episode "Utopia" the Doctor learns that the Master survived. The Doctor failed to sense him because he used a chameleon arch to turn himself into a human (as the Doctor did in "Human Nature"), while hiding at the end of the Universe. The Master's subsequent conquest of 21st century Earth and his attempt to set up a new, expansionist Time Lord empire, is foiled by the Doctor and his companion Martha Jones. Shortly after his plan fails, the Master is shot by his human wife Lucy Saxon, and, refusing to regenerate, dies. The Doctor burns his body on a pyre. ("Last of the Time Lords").
In the episode "The Doctor's Daughter", after landing on planet Messaline the Doctor was forced to place his hand inside a progenation machine, which used his DNA to create a new soldier, to fight in the war taking place. The new female soldier - his daughter, Jenny, possesses the DNA of a Time Lord. While the Doctor argues that a Time Lord is more than simply genetics, he is impressed by the superhuman abilities she displays, and intelligence on par with his own. By the end of the episode he becomes more willing to accept her as his daughter and a Time Lord. The Doctor states that a Time Lord is more than simply DNA, but nevertheless, the Doctor's species now lives on in some form. Donna Noble also gains the mind of a time lord or at least part of the Doctor's. After being trapped on the TARDIS as it is about to be destroyed, she is drawn towards the Doctor's hand, which was severed in the 2006 Christmas special and loaded with unused energy from a partial regeneration (see "Journey's End", 2008). Touching the hand triggers the remaining regeneration process, and causes a second Doctor to be created, one who is part human, borrowing traits from Donna just as she absorbs part of his mind.