Spy Master

Regenerating into a new body, the Master discovered that the entire Time Lord history had been "built on the lie" of the Timeless Child, as well as the true origin of the Doctor, in the Matrix. Embittered by his discoveries, and lashing out from the belief he was indeed inferior to the Doctor, the Master took his revenge on Gallifrey, leaving it in ruin.

Wanting to inform the Thirteenth Doctor of his discovery, the Master worked with a race called the Kasaavin and tech billionaire Daniel Barton in a plot to wipe out humanity. His plan was thwarted at the last second by the Doctor, and the Master was imprisoned in the Kasaavins' realm.

The Master eventually escaped and returned to reveal the truth about the Timeless Child to the Doctor and build an army of CyberMasters from the remains of the Time Lords he had killed. His plot was thwarted when Ko Sharmus detonated the death particle on Gallifrey, apparently killing the Master and his CyberMasters.

Early life
After regenerating into a new incarnation, the new Master returned to their dark ways, looking down on Missy for trying to better herself and spending so much time with the Doctor. (PROSE: The Doctor vs the Master)

Hacking into the Matrix on Gallifrey until he "got lost", (TV: The Timeless Children) this incarnation of the Master learned the truth of the Timeless Child; (TV: Spyfall) the Doctor was the Child, having been found and adopted by the Shobogan explorer Tecteun, as well as the root of regeneration and the foundation of the Time Lord society. Enraged that the Doctor's childhood attitude of being "special" was apparently validated, (TV: The Timeless Children) the Master decided he had to "make them pay"; he ravaged Gallifrey and left the Citadel in a flaming ruin, having apparently killed all of the Time Lords. (TV: Spyfall) However, he chose not to destroy the Matrix. (TV: The Timeless Children)

Alliance with the Kasaavin
Wanting to send a message to the Doctor about what had transpired on Gallifrey, the Master found a species known as the Kasaavin from another dimension had embedded across the universe as sleeper agents. Brokering an alliance with them, the Master recruited Daniel Barton into his plan to trap the Doctor by proposing that Barton and the Kasaavin turn the human race into hard drives. As part of the plan, the Master arranged for "The Silver Lady" to be delivered to Charles Babbage, and that it was passed on to those who would influence the development of computers through history until it ended up with Barton. The Master used his Tissue Compression Eliminator to kill a newly-recruited MI6 agent on his first day, and took his place. He was put to work as an analyst known as "Horizon Watcher", and given the codename "O" as a joke on how his superior, "C", would react to his presence. During his time at MI6, the Master crossed paths with the Doctor prior to her thirteenth incarnation. Not recognising the Master, the Doctor stayed in contact with "O" via text messages. "O" was eventually sacked by C sometime prior to 2020, and the Master went into hiding in Australia, using his TARDIS as a hideout.

By 2020, the Kasaavin began to attack spies from different agencies all across the Earth once the intelligence services started to realise their presence, leading MI6 to track down the Thirteenth Doctor. While the Doctor was at MI6's HQ, the Master personally assassinated C, and the Kasaavin forced the Doctor and her friends to flee to "O"'s alleged location in the Great Victoria Desert. Upon their arrival, "O" greeted the Doctor and Graham O'Brien. He assisted the Doctor by sharing his findings and, after a staged Kasaavin attack, travelled with Team TARDIS to confront Barton.

At Barton's party, "O" blended in with the other guests until Barton fled, making the team pursue him to an airport. As Barton was about to take off, the team ran to the plane, with "O" almost not catching up, using the excuse that he was terrible at sprinting. This triggered the Doctor's suspicion, as "O"'s file said he was a champion sprinter. After being confronted over the inconsistency, the Master revealed his true identity, even showing Team TARDIS the shrunken corpse of the real "O". He then revealed he had been working with Barton and the Kasaavin, and left Team TARDIS on the plane as he detonated a bomb in the cockpit. Alerted to the Doctor's survival by Barton, the Master followed her to 1834 London, where he held a crowd at the Royal Adelaide Gallery hostage to draw out the Doctor. However, after a brief conversation with her, the Master was forced to flee when attacked by Ada Gordon.

The Master next chased the Doctor and Ada to 1943 Paris, where he set himself up as a German officer using a Teutonic psychic perception filter to hide his non-Aryan appearance from the Nazis. Once the Doctor made contact with him, the Master met her atop the Eiffel Tower, where he revealed his real plan had been to get the Doctor's attention and persuade her to return to Gallifrey. However, the Doctor had had Noor Inayat Khan leak information to the Nazis of the Master being a double agent, and, as they came to arrest him, deactivated the perception filter to ensure his capture while she stole his TARDIS. After seventy-seven years of waiting, the Master finally caught up to Team TARDIS back in 2020, just as the Kasaavin were enacting their invasion. However, the Doctor thwarted the Master's plot and exposed to the Kasaavin the Master's plan to betray them and Barton. Furious, the Kasaavin captured the Master, trapping him in their reality. (TV: Spyfall)

With the psychic link between him and the Doctor still active, the Master, sometime later, was pressured into a mental conversation with her, during which they looked back on the state of their relationship and, as it were, "how it had all gone wrong". The Master once again taunted the Doctor with the knowledge he held over her, saying that he would only reveal it when he was "good and ready", and ended the chat. (PROSE: The Doctor vs the Master)

Joining with the Cyberium
Eventually, the Master was able to escape the Kasaavin, and returned to Gallifrey. He emerged from the Boundary when the Doctor and Ryan Sinclair arrived on the Planet of the Boundary. (TV: Ascension of the Cybermen) By threatening Ryan, Ethan and Ko Sharmus with his Tissue Compression Eliminator, the Master was able to force the Doctor to accompany him to the ruins of Gallifrey. Leading the Doctor into the Citadel, the Master reminisced about their times together there, before calling Ashad and inviting the Cybermen to Gallifrey.

Refusing her pleas to save her friends from the Cybermen, the Master trapped the Doctor in a paralysis field, telling her it was time for her to learn the truth of the Timeless Child. The Master sent the Doctor deep into the Matrix, accompanying her via a mental projection. Inside the Matrix, the Master showed the Doctor the history of Tecteun and her adopted daughter who underwent the first regeneration after falling from a cliff in a terrible accident, and was experimented upon for years to discover the secret of the power until Tecteun eventually gained the ability to regenerate and shared it with others of her race, who renamed themselves "Time Lords". The Master then explained that the Doctor herself was the Timeless Child in a life from before her first incarnation, the Time Lords having erased their memory to create a "great creation myth" for themselves.

Back on Gallifrey, the Master greeted Ashad, who revealed that he intended for his new army to destroy all organic life in the universe using a death particle, created using the Cyberium. However, the Master was less than pleased to learn that Ashad intended to turn the Cybermen into a fully-autonomous race, and offered Ashad another solution to becoming the dominant race in the universe. Taken to the Cybercarrier, the Master examined the cyber-conversion chambers and killed Ashad to acquire the Cyberium, though realised that the death particle was still usable from Ashad's remains and could be used as a weapon. He offered the Cyberium an alliance by combining all of the knowledge of the Cybermen with all of the knowledge of the Time Lords that he had absorbed from the Matrix, which caused the Cyberium to take him as a host. Using the bodies of the Time Lords he had killed on Gallifrey, the Master intended to use them to create a new race of Cybermen capable of regenerating, which he dubbed the "CyberMasters".

Sensing that the Doctor had escaped the Matrix, the Master telepathically led her to Ashad's remains. After sending the humans back to Earth in a TARDIS, the Doctor met with the Master in the Matrix chamber, where he revealed to her that he was the host of the Cyberium. Though he was impressed by the Doctor's resolve in the face of the Timeless Child revelation, the Master goaded the Doctor to detonate the death particle he had led her to, and was not surprised when she couldn't do it. As the Master gloated over the Doctor's "weakness", Ko Sharmus entered, intending to sacrifice himself to ensure the destruction of the Cybermen. The Doctor escaped in another TARDIS, while the Master ordered his CyberMasters to kill Ko Sharmus. However, Ko Sharmus was still able to detonate the death particle in his final moments. Before it could be detonated, the Master ordered the CyberMasters to follow him elsewhere. (TV: The Timeless Children)

Psychological profile
Believing "a little chaos [to be] a wonderful thing", (TV: Spyfall) the "Spy" Master could fall into unpredictable fits of rage, stating he could "relate" to a short-fused bomb, (TV: Spyfall, The Timeless Children) to the point that he once attempted to strangle the Thirteenth Doctor with his bare hands. After taking a crowd hostage, he spontaneously focused on a cowering woman and demanded to know if she had moved, only to apologise for his "mistake" before killing her with the TCE. (TV: Spyfall) The Master once voiced a belief that nothing could "calm all [his] rage", though the Doctor countered her belief that he was actually "scared of everything". (TV: The Timeless Children)

The "Spy" Master enjoyed playing long games, like tricking the Doctor into believing he was "O", gleefully clapping his hands at the Doctor's inability to deduce who he was despite giving clues and expressing he had had "a lot of fun" when she finally realised he had fooled her. (TV: Spyfall)

While not above working with others to achieve his goals, the Master did not see his partners as equals, but as assets to use for his own gain and dismiss once they had served their purpose. (TV: Spyfall, The Timeless Children) His arrogance was so profound that he did not even attempt to conceal his TARDIS in 1943 Paris, (TV: Spyfall) and felt he was justified in destroying Gallifrey when he learnt that the Time Lords owed their existence to the Doctor, himself included. (TV: The Timeless Children)

Believing he had no "better nature", (TV: The Timeless Children) and looking down on Missy deciding to better herself, (PROSE: The Doctor vs the Master) the "Spy" Master had a passion for killing others, remarking how it gave him a "buzz", and that it felt right in his hearts to do so. (TV: Spyfall) His disregard for life was so great that he even threatened to kill to prove a point. (TV: The Timeless Children) His passion for death, when infused with anger, was reawakened in him when he discovered the lies about the Timeless Child that the Time Lords had committed, driving him to commit genocide back on Gallifrey. (TV: Spyfall)

Despite not wanting her as his enemy again, the Master loved playing mind games on the Doctor and treating her as an inferior, (TV: Spyfall, The Timeless Children) having her kneel before him when he was holding hostages. He chased her through time to force her to listen to him just to get a message across, but would express rage when she outsmarted him. He also looked down on her companions, likening his apparent killing of them to "swat[ting] flies".

However, beneath his charismatic exterior, the "Spy" Master hid a melancholy pain, recounting his ravaging of Gallifrey with sombre calm, though he was still petty enough not to divulge the entire truth of the Timeless Child to the Doctor, reasoning it should be as difficult for her to discover the truth as it was for him. He was also unnerved by the sounding of a four-beat rhythm that resembled "the Drumming". (TV: Spyfall)

When Ashad's death particle failed to activate upon his death, the Master found himself disappointed and noted his acceptance should it have killed him. He later tried to persuade the Doctor to detonate the death particle to kill him and his CyberMasters. (TV: The Timeless Children)

Taking the Doctor's body
(Herein, summarize the events of The Power of the Doctor.) The Master hatches a plot with the Daleks and the Cybermen. Using Time Lord technology, the Master takes possession of the Doctor's body --forcing it to regenerate into a copy of his current incarnation. Now possessing the Doctor's body, he pretended to be the Doctor to drag her name through the mud. However, Yaz and Vinder forced the Master back into the machine and reversed the process. Now damaged from his experiment, the Master shot the Thirteenth Doctor as revenge. (TV: The Power of the Doctor)

Appearance
This incarnation of the Master was a short-standing, skinny man with dark skin, black hair, and brown eyes. He originally had stubble as "O", but once he revealed his true identity, the Master grew out a full beard. He regularly disguised himself as various individuals, such as an auction dealer and even a Nazi officer, shaving his hair off for the latter.

After being stranded on Earth for seventy-seven years, the Master took to wearing a double-breasted overcoat of plum purple Donagel tweed, with external pockets on each hip and a chest pocket skewed at a forty-five degree angle under the left lapel, and metallic silver buttons attached to the coat; two on each side pocket, one on the breast-pocket, two on each sleeve, two on the back strap, and three on the front right side.

He also wore a plaid moleskin waistcoat and trousers with a pattern of three vertical stripes interlocking with three lines of horizontal dashes, in varying shades of orange over a navy background. The waistcoat additional possessed two blue chains, silver shank buttons and black style lapels. The end of his trouser legs were turned up slightly. Completing his ensemble was an indigo shirt, purple knee-high socks, and low topped leather lace-up shoes. (TV: Spyfall)

Behind the scenes
to be added