The Matrix

The Matrix, officially called the Matrix of Time, (TV: Mindwarp, PROSE: The Quantum Archangel) or sometimes the APC Matrix Net, (PROSE: The Cyber Files) was a supercomputer, a micro-universe used by the High Council of the Time Lords as a storehouse of knowledge to predict future events, maintained by the Keeper of the Matrix.

As TARDISes possessed their own matrix, every Time Lord and TARDIS was connected to the central Matrix on Gallifrey where their experiences were constantly being uploaded. (COMIC: Sky Jacks, AUDIO: Songs of Love) For this reason, the Eighth Doctor described the Matrix as "the sum total of all Time Lord experience". (AUDIO: Lies in Ruins) called it "the lived history of our race". (TV: The Timeless Children)

Characteristics
The Matrix, specifically, contained a simulated reality environment, once described as a "micro-universe" (TV: The Ultimate Foe) which stored the personalities of Time Lords, now without physical bodies, and even the past (COMIC: The Forgotten) or future incarnations of living Time Lords (AUDIO: Ascension) within the APC Net, which cross-checked the data within the Matrix. (AUDIO: The Inquiry)

As the largest possibility engine ever built, (AUDIO: Lies in Ruins) the Matrix could even store consciousness. This connection went both ways, allowing all recorded Time Lords on one occasion to be "reset" to a past data point through their biodata. (AUDIO: Ascension) A Time Lord could also use the Matrix to project their image onto real spacetime, or at least within a TARDIS, in order to send a message. (AUDIO: Songs of Love)

The Matrix functioned both as a "crypt" and a stone circuit board, and used Cloister Wraiths and "filed" Daleks, Cybermen and Weeping Angels attached to living "fibre optic cables" to guard the Cloisters as a "firewall". It could also ring the Cloister Bells in the event of impending catastrophe. (TV: Hell Bent)

Matrix data slices served as hard-drives that contained the virtual reality, (TV: Dark Water) which could also be projected around individuals, described by Coordinator Narvin as immersion in the five-dimensional episodic interface of a Panoptric network. The Eighth Doctor was impressed he didn't need to wear "silly plastic glasses". (AUDIO: The Death of Hope)

Romana II explained that when connected to the Matrix, the user was outside of real spacetime, "alone on the astral plane". (AUDIO: The Inquiry)

All Time Lords were connected to the Matrix on a basic level, (AUDIO: Pandora) and the Matrix stored the memories of dead Time Lords in a framework of electrochemical cells. (TV: The Deadly Assassin)

It was not only a record of the past, but could predict the future as well (TV: Arc of Infinity) by generating prophecies out of algorithms. (TV: Hell Bent)

The amount of knowledge in the Matrix, though vast, was not complete, and could be tampered with, given access. The unauthorised extraction of a Time Lord's bio-data from the Matrix was an offence tantamount to treason. (TV: Arc of Infinity)

A particularly skilled person such as the Valeyard could create images of events that never had happened nor ever would. (TV: Mindwarp, Terror of the Vervoids, The Ultimate Foe)

Whenever anyone used the Matrix to acquire a specific piece of information, a safeguard would cause anything else the user accidentally stumbled across to be wiped from their minds. (PROSE: Timewyrm: Genesys)

If two or more incarnations of the same Time Lord accessed the Matrix simultaneously, they all gained equal access to all other incarnations' memories. Because of this, a young, pre-Key to Time version of Romana I instantly understood her future when Lady President Romana II joined her in the Matrix. Additionally, sections of the Matrix could be partitioned, trapping entities in sections cut off from the rest of the Matrix. (AUDIO: Lies) Following the Last Great Time War, the length of the Matrix's database was eclipsed by the Dalek pathweb, leading the Twelfth Doctor to identify a unknown face through the latter. (TV: Twice Upon a Time)



Environment
To living beings, the Matrix could appear like conventional reality, (TV: The Deadly Assassin, The Ultimate Foe) a surreal dream, (COMIC: The Tides of Time) a dark void with lines of light, (TV: Arc of Infinity) or first one, then the other. Physical laws were malleable to the will of the inhabitant. Experience and sheer will gave one control over "reality". For example, the Fourth Doctor shouted, "I reject it," and his wounded leg instantly healed; this was undone by a more skilled Time Lord. (TV: The Deadly Assassin)

Beings known as the Matrix Lords, including Rassilon himself, "lived" there and could direct actions in the universe. They created a physical agent, Shayde, to act for them in the outside world. (COMIC: The Tides of Time)

Physical access
Early in Rassilon's reign as Lord President, he accessed the Matrix through a portal in the Great Hall of Time. (PROSE: Snow White and the Seven Keys to Doomsday)

Living beings could access the Matrix via the Matrix Chamber, (AUDIO: Neverland, TV: The Timeless Children) or through the use of an apparatus connected to the user's head. (TV: The Deadly Assassin) The Crown of Rassilon worn by any Time Lord gave them instant access. (TV: The Invasion of Time) The Keeper of the Matrix held the Key of Rassilon, granting access to the Seventh Door, thought legendary until the Doctor used the Key to access it. The Seventh Door allowed physical access to the Matrix. (TV: The Ultimate Foe)

Knowledge
Information was added to the Matrix, being imprinted on the nexus, as it was discovered by Time Lords, (AUDIO: The Wings of a Butterfly) being organised by the recorders living within the Matrix. (AUDIO: Neverland) Additionally, all events that occurred in the Capitol were recorded in the Matrix, (AUDIO: The Inquiry) and it also received data from sensors in TARDISes, (PROSE: The Quantum Archangel) seeing through each and every TARDIS' "eyes". (AUDIO: Songs of Love)

Many facts, figures, and formulas were contained within the Matrix, including faster-than-light travel, anti-gravity power, dimensional transference, (TV: The Mysterious Planet) how to build the De-mat Gun, (TV: The Invasion of Time) the threat posed by the Timewyrm, (PROSE: Timewyrm: Genesys) quantum mnemonics from the pre-universe, (PROSE: Millennial Rites) the Spinward Corporation and Arcadia in the 25th century, (PROSE: Deceit) America in the 1950s, (PROSE: First Frontier) history from the Humanian, Sensorian, Sumaran, and Rassilon Eras, (AUDIO: Neverland) and the Sanctuary on Bukol. (PROSE: The Golden Door) During the Last Great Time War, there was a Matrix file on the Sensorites. (AUDIO: Sphere of Influence)

Darker knowledge contained within the Matrix included the doomsday weapon on Uxarieus, (TV: Colony in Space) the Earth's sleeping races, (TV: The Sea Devils) the mechanics of the Source of Traken, (TV: The Keeper of Traken) the location of the Nestene homeworld, (TV: Terror of the Autons) the name of the last of the Dæmons, (TV: The Dǣmons) the deathworms, (TV: Doctor Who) the Crystal of Kronos and its relationship with the Chronovores, (TV: The Time Monster) the army of Daleks on Spiridon, (TV: Planet of the Daleks) the Martian GodEngine, (PROSE: GodEngine) the psychic parasites of Bellerophon, the frozen gods of Volvox, the political machinations of the Amentethys, the Proculus and their offspring the Scerbulus, the forgotten knowledge of the Kirbili, and limited information on the Constructors of Destiny concerning the Midnight Cathedral. (PROSE: The Quantum Archangel)

There was also a section of the Matrix known as the Slaughterhouse, compiled by the Celestial Intervention Agency, which contained a whole armoury of theoretical weapons, including the Profane Virus of Rassilon and, in a parallel universe, the Armageddon Sapphire. (PROSE: The Quantum Archangel)

The Matrix contained information on the true history of the Timeless Child and some information on the Division. However, great portions of this information were redacted even beyond 's ability to recover. In addition, the Matrix contained the story of Brendan, an immortal Irish policeman and an analogue for the story of the Timeless Child. It was suggested by the Master that the Second Tecteun hid Brendan's story for her child to find as a gift or an apology and a way for the Timeless Child, now the Doctor, to decode the truth of their own existence. (TV: The Timeless Children)

Creation
Rassilon set up the Matrix in the Dark Times, early in his Presidency. (PROSE: Snow White and the Seven Keys to Doomsday) It was thought to be his last great invention, born out of a desire to preserve the knowledge of deceased Time Lords for future generations to consult. (PROSE: A Brief History of Time Lords)

According to one account, the Matrix was actually originally a part of the APC Net rather than the other way around, but over the millennia, the Matrix grew to outstrip the APC Net by far until it was the APC Net that was considered a section of the Matrix. (PROSE: Gallifrey: A Rough Guide)

A separate account stated that it was the Matrix itself that had created the Time Lords, but only to act as creators to it and its children, whose existence beyond standard time meant they had always existed. When confronting her sister in the build up to the War, Lolita described the Matrix's engineering of the Time Lords as pandering; a pointless attempt to justify its existence by retroactively giving itself an origin. The TARDIS was quick to point out that it was possible both species' creation of the other may have occurred simultaneously. (PROSE: Toy Story)

Uses of the Matrix
After it was first set up, Rassilon used the Matrix to ask who had the power to make Gallifrey fall. (PROSE: Snow White and the Seven Keys to Doomsday) The Matrix answered by foreseeing the existence of the entity known as the Hybrid, a creature crossbred from two warrior races that would one day stand in the ruins of Gallifrey and break a billion billion hearts to heal its own, unravelling the Web of Time in the process. (PROSE: A Brief History of Time Lords) According to the Dalek Combat Training Manual however, the Time Lords only learnt of the prophecy of the Hybrid during the Cloister Wars. (PROSE: Dalek Combat Training Manual)

The Surgeon once remarked that the "matrix of crystals" with which the Superiors clung onto life was one of the reasons they remained the main power of the universe during the time before the War in Heaven (PROSE: The V Cwejes)

stole from the Matrix all the knowledge he needed to make his various schemes on 20th century Earth against the Third Doctor possible. (PROSE: The Quantum Archangel, A Brief History of Time Lords)

Returned to Gallifrey by Councillor Goth, used the Matrix, secretly infiltrating it and using Goth as his agent within it. Goth confronted the Fourth Doctor there and attempted to kill him. (TV: The Deadly Assassin)

As Lord President, the Doctor used the Matrix to gain access to the secrets needed to defeat the Sontaran invasion of Gallifrey, specifically the De-mat Gun. (TV: The Invasion of Time) While connected to the Matrix, he learned of the existence of the Timewyrm (PROSE: Timewyrm: Genesys) and quantum mnemonics. (PROSE: Millennial Rites)

After his supposed execution to stop Rassilon's exiled contemporary Omega from returning to the universe of matter, the Fifth Doctor hung suspended in the Matrix. Omega also had access to the Matrix. (TV: Arc of Infinity) One of the many versions of Clara Oswald created after she entered the Doctor's time stream appeared in the Matrix and saw the Fifth Doctor when he was sent there. (TV: The Name of the Doctor)

The Valeyard established a stronghold, the "Fantasy Factory", in the Matrix as part of his plan to steal the Sixth Doctor's remaining regenerations. During his attempt to stop him, the Doctor, as well as, entered into the "dreamscape" therein, the latter taking his TARDIS (or an illusory version of it) there. The Valeyard somehow took over the Keeper of the Matrix. (TV: The Ultimate Foe)

The Seventh Doctor confronted the Dark Matrix, which was trapped inside a TARDIS as it imploded. (PROSE: Matrix)

During the Last Great Time War, the Eleventh General created the Dalek Combat Training Manual by uploading the Doctor's various encounters with the Dalek race to a subset of the Matrix, even using the computer's processing power to extrapolate post-Time War encounters between the Doctor and the Daleks, for the Time Lord infantry to consult and be aware of the Daleks' weaknesses. (PROSE: Dalek Combat Training Manual)

Fate of the Matrix
An ancient Gallifreyan evil named Pandora also survived and emerged from a special partition within the Matrix. Lady President Romana was eventually able to destroy the entity by seemingly destroying the Matrix itself. (AUDIO: Warfare) However, Romana later discovered that it had only been damaged. (AUDIO: Ascension)

After Gallifrey was destroyed by the Eighth Doctor in the War in Heaven, the Time Lords survived within the Matrix, which had been downloaded into the Doctor's mind - although he had to sacrifice much of his memory to make space for it. The reconstruction of the Matrix (and, thanks to it, of the Time Lords and Gallifrey) was possible, but required a sufficiently advanced computer. (PROSE: The Gallifrey Chronicles)

Surviving the Last Great Time War
The Matrix disappeared with Gallifrey at the end of the Time War. (AUDIO: Divorced, Beheaded, Regenerated) However, two seemingly incompatible accounts existed as to the circumstances in which it actually survived the last day of the Time War.

The Hypothetical Gentleman
According to one account, in the final moment of the Last Great Time War, the deaths of every Time Lord being uploaded to the Matrix at once allowed it to gain sentience. However, the resulting entity immediately realised it was trapped on a planet doomed to destruction, within instants. However, being connected to every TARDIS, the Matrix managed to escape its fate by uploading the entirety of itself into the one surviving Gallifreyan timeship in its reach — the Doctor's TARDIS. Having been born of innumerable deaths, the Matrix was, by the Doctor's later analysis, insane, wishing death and destruction on the rest of the universe out of spite. The Matrix intended to complete Rassilon's Final Sanction, unravelling the Web of Time and ending Creation itself, however, the TARDIS sensed its intentions through their connection and worked to keep the stowaway contained. Connected to the minds of the Doctor and his TARDIS, the Matrix remained a prisoner, scheming for centuries a way to break out into the wider universe. (COMIC: Sky Jacks)

Exploiting the telepathic circuits of the Doctor's TARDIS, (COMIC: Sky Jacks) the Matrix projected images of a quantum resonator into Emily Fairfax's mind, convincing her and her husband that she was being contacted by an angel. After the pair built the machine, the Matrix linked it to the TARDIS to power it. The Matrix, now in humanoid form, emerged from the machine to find a police officer, whom he sucked the time out of, leaving him frozen in time. The Eleventh Doctor witnessed this and decided to investigate the machine's power source. The Hypothetical Gentleman, as dubbed by the Doctor as he mistakenly believed the "man" had come from a hypothetical universe linked to by the quantum resonator, then proceeded to suck out the time from Rory Williams. When the telepathic Emily read the Gentleman's mind, it was filled with images of Sontarans, a peg doll, a Zygon, a Kroton, a Headless Monk, a Silent, a Weeping Angel, and a Krynoid.

He subsequently sucked the time out of Charles, deeming the meal, "an insufficient morsel", and then disappeared. The Doctor was examining the victims, when he returned, and the Doctor him about how he could write in High Gallifreyan. The Gentleman didn't provide an answer, and instead taunted the Doctor with the unknown knowledge. He then promptly began to steal the Doctor's time, which would have given him his own reality, but Amy Pond smashed the quantum resonator, apparently sucking him back into his hypothetical world and freeing all his victims. As the Doctor, Amy, and Rory tried to leave in the TARDIS, the control panel sparked, surprising the Doctor, and he described it as the TARDIS having an upset tummy, and that it was nothing to worry about. In truth, the Hypothetical Gentleman had been returned to the TARDIS and its presence continued to upset the timeship. (COMIC: Hypothetical Gentleman)

The Matrix attempted to fight the Doctor's TARDIS for control of its systems, and succeeded in taking control of one the TARDIS's old console rooms. From there, the Matrix programmed the creation of a large and featureless room featuring a copy of the TARDIS's outer police box shell, thereby manipulating the Doctor into believing he had left the TARDIS when he walked out of those doors. The Matrix then took control of the TARDIS's power source, the Eye of Harmony. Using the Eye's power, the Matrix created a wormhole to escape into the wider universe. However, the TARDIS retaliated by expanding the console room controlled by the Matrix to massive size, making it so absurdly big that it contained an entire "sky world". This process, which the Matrix could not stop, diverted enough energy from the Eye that the Matrix could no longer use any for its own purposes.

The wormhole, running in the direction opposite to that wished by the Matrix, drew in aircrafts and starships from various points in space and time and trapped them inside the "sky world", alongside the Matrix itself as well as he Doctor and his companion Clara Oswald. While in the sky world, the Matrix built itself several spider-like robotic bodies, as well as an army of pterodactyl-like robots, out of the scrap metal provided by the various crashed spaceships. Just as it seemed to make its escape using an atomic bomb brought to the sky world in the American aeroplane Sky Jack, the Matrix was stopped by the Doctor, who trapped the mad intelligence forever by connecting both ends of the wormhole together into an ouroboros shape. (COMIC: Sky Jacks)

The Matrix on Gallifrey
According to another account, Gallifrey and the Time Lords were not actually destroyed by the Moment, despite the widespread belief of the rest of the universe; the planet had instead been placed, Matrix and all, into a pocket universe, hidden but unharmed. (TV: The Day of the Doctor) Scanning for N-Space, the Matrix discovered the time field, giving the Time Lords an opening through which to broadcast the Question. (PROSE: A Brief History of Time Lords) After Gallifrey returned to the universe, the Twelfth Doctor found the Matrix where he remembered it from his childhood, below the Capitol, accessible the Cloisters. An imprisoned Dalek encountered by the Doctor and Clara Oswald on their way to the Matrix seemed to the Doctor to have been there since the Cloister Wars. (TV: Hell Bent)

Some time later,, sent back to Gallifrey just prior to its supposed destruction, spent some time in a Gallifreyan hospital before leaving the planet in what the renegade later described as a "mutual kicking me out". Having therefore recently visited Gallifrey, the Master's next incarnation,, (TV: The Doctor Falls) was able to use a Matrix data slice to store the minds of the recently deceased into a data cloud so that the emotions could be altered and upgraded once their minds were downloaded back into converted Cybermen. (TV: Dark Water, Death in Heaven)

In order to find out about Testimony, the Twelfth Doctor suggested using the Matrix on Gallifrey. However, he decided instead to use the Dalek Pathweb through Rusty as they needed something bigger than the Matrix. (TV: Twice Upon a Time)

At some point after the events on the Mondasian colony ship, (TV: World Enough and Time, The Doctor Falls) returned to Gallifrey where he began playing around and hacking into the Matrix. The Master got lost inside before he found "everything" and later told the Cyberium that he "ransacked" the Matrix and as a result, had all of the knowledge of the Time Lords inside his head. What the Master learned from the Matrix about the Timeless Child and the truth about the Time Lords' history caused him to ravage Gallifrey. (TV: Spyfall, The Timeless Children)

After returning to the ruins of Gallifrey with the Thirteenth Doctor, the Master revealed that he left the Matrix intact when he destroyed everything else. The Master used the Matrix to show the Doctor the truth about the Timeless Child, Tecteun and the Time Lords, but revealed that large portions of the Matrix's data relating to the life of the Timeless Child - in reality the forgotten past of the Doctor - and the Division had been erased even beyond the Master's ability to recover despite the fact that it had taken up a lot of space in the Matrix. The Master suggested that the images of Brendan, the disguised true story of the Timeless Child which he had transmitted into the Doctor's mind, were purposefully left behind by Tecteun as a gift or apology to her child, possibly as a way to decode and learn the truth about their past.

After revealing his new race of CyberMasters, the Master then trapped the Doctor inside the Matrix. Guided by a Matrix projection of a forgotten incarnation, the Doctor overloaded the Matrix with a blast of her memories, forcing it to release her. (TV: The Timeless Children)

Other realities
In an alternative timeline the Matrix was invaded by the Cybermen. (COMIC: Prologue: The Sixth Doctor)

In one of the infinite parallel universes of "possible space", (COMIC: Fire and Brimstone) the Matrix was located in the Panopticon. It was the Time Lords' "record of all life in the Universe", in which they recorded "the significant events on the planets of [their] Galaxy and beyond". (PROSE: The Chronicles of Doctor Who?)

In a parallel universe, the Valeyard won his battle with the Sixth Doctor within the Matrix, merging with him and gaining his remaining regenerations. When the Valeyard began altering history, Coordinator Vansell and the President took Mel inside the Matrix to observe, however became trapped there after the Valeyard destroyed Gallifrey with the Doomsday Weapon. Vansell gave Mel a time ring to escape so she could pursue the Valeyard. (AUDIO: He Jests at Scars..)

Behind the scenes

 * In Steven Moffat's script for Hell Bent, when the Twelfth Doctor meets Me on the last fragment of Gallifrey at the end of the universe, she tells him that the Matrix has survived, though it is now "guttering", and that its ghosts sometimes tell her stories about "the little boy who didn't know how to give up". This dialogue was omitted from the broadcast version.