The Master (Scream of the Shalka)

In one potential future for the Master, at some point after, he forged an alliance of sorts with the Ninth Doctor, who gave him a new lease of life in the body of an android bound to the TARDIS.

The ghost in the machine
, after an attempt to steal the Eighth Doctor's remaining regenerations, fell through the Eye of Harmony and bounced throughout the Time Vortex. (TV: Doctor Who) Having passed through the Eye of Harmony inside the Doctor's TARDIS, the Master's essence remained trapped as an echo within. During his imprisonment, the Master could converse with the Doctor, attempting to tempt him to take actions that he would not otherwise take. (PROSE: The Gallifrey Chronicles)

Though he had no corporeal form, he manifested himself through screens and mirrors, though the Eighth Doctor was unsure of the identity of "the ghost in the machine". (PROSE: Sometime Never..., The Deadstone Memorial, The Gallifrey Chronicles)

Last chance for salvation
According to some accounts, the Master escaped the Doctor's TARDIS with an established corporeal form some time later. Eventually, the Master and the Ninth Doctor crossed paths in the flesh. The Master aided the Doctor in repelling the alien foe responsible for invading Gallifrey and the death of the Doctor's previous companion. It was during this encounter that the Master was left damaged and without a suitable body. (PROSE: Doctor Who - The Ninth Doctor) However, according to one Time Lord historian, some had at least speculated that the Doctor had simply built the android body for the Master as a result of his death falling through the Eye of Harmony. (PROSE: A Brief History of Time Lords)

At any rate, in return for his aid, the Doctor offered to transfer the Master's mental resources into an android body, the appearance of which the Master could personally select. (PROSE: Scream of the Shalka) The Master accepted, though he would later remark this was a foolish choice. (WC: Scream of the Shalka) While this body granted him corporeal form, he was limited to the confines of the Doctor's TARDIS as his android body was purposely designed to never be able to leave the ship. (PROSE: The Feast of the Stone) In his new home, the Master served as the TARDIS Defence System. (WC: Scream of the Shalka) Now bound to travel with the Doctor, the pair was sent to work for the Doctor's unseen superiors to solve the dangerous problems that plagued the universe. (INFO: Scream of the Shalka)

Travelling with the Doctor
When the Doctor hosted a party in the TARDIS control room, the Master's face fell into a soup tureen, as the catches that kept it attached to the complex machinery that lied beneath were loose. The Master, embarrassed, had to fish his face plate out with a pair of silver tongs. (PROSE: Scream of the Shalka)

Joined by Alison
The Master assisted the Doctor and Alison Cheney in fighting the Shalka. When the conflict was over, the Master convinced Alison to travel with them in the TARDIS as a companion. (WC: Scream of the Shalka)

When the TARDIS arrived in a dank cavern, the Master broke the Doctor free of a psionic force that caused him and Alison to experience a bombardment of traumatic and emotional memories. It was eventually discovered that the Master's memories were being fed into Alison's mind so the psychic vampire could feast off her emotions. While his body was shut off in an attempt to save Alison, the Master was eventually connected to the TARDIS' telepathic circuits by the Doctor in order to destroy the psychic vampire; the Master's pure evil memories and personality being too much for the creature. (PROSE: The Feast of the Stone)

Eventual fate
According to one account, the Master's mind was eventually ripped out of the TARDIS by the Time Lords so that they could, a process which left the TARDIS console damaged. (PROSE: Doctor Who and the Time War) He went on to fight in the Last Great Time War, witnessing the Dalek Emperor's takeover of the Cruciform, (TV: The Sound of Drums) in a body somewhat similar to the android's appearance, albeit with fairer hair and a different cut of beard. (TV: Utopia; AUDIO: Only the Good)

However, according to other accounts, the version of the Eighth Doctor's future where he became the pale-faced gentleman was a different future from the one that ultimately led to the Northern chap with big ears, (PROSE: The Tomorrow Windows) even if these two Ninth Doctors and a third one were equally real. (PROSE: The Gallifrey Chronicles) Accounts dealing with the Last Great Time War further depicted the Master's resurrection by the Time Lords in starkly different circumstances, with the fair-haired "War" Master resembling the android not even being the body he was first resurrected in. (AUDIO: Day of the Master) There existed some degree of uncertainty among post-War Time Lord historians as to precisely when in his timeline the Time Lords had resurrected the Master, with some going as far as to suggest that they had simply plucked him from the moment he had fallen into the Eye of Harmony, skipping over any later developments altogether. (PROSE: A Brief History of Time Lords)

Psychological profile
The "Android Master" retained his charm and wit, together with his hypnotic abilities. Remaining loyal only to himself, the Master would lie about his motivations and join with whomever could offer him an advantage to his current situation. He attempted to hypnotise Alison Cheney, but was interrupted by the Doctor.

The Master and the Doctor, forced to cohabitate in a way that ran counter to much of their previous lives, shared an antagonistic relationship. He would feign annoyance at the Doctor's various "human" traits, and was resentful of the nature by which he lived, even commenting that death would have been a better fate for him than listening to the Doctor "being right all the time". (WC: Scream of the Shalka)

Despite this, the Master clearly cared for the Doctor. When the Doctor returned from his presumed death at the hands of the Shalka, the Master's face lit up with delight. (PROSE: Scream of the Shalka) Likewise, he was aware of the Doctor's loneliness, and talked Alison into becoming his companion, despite admitting to disliking her. (WC: Scream of the Shalka)

While he had chosen the look of his body and the voice that it produced, the Master did not enjoy reminders of his current nature as "a mind contained inside a program, [and] a program contained within a machine." (PROSE: Scream of the Shalka)

Appearance
The Master's android body resembled a mature man with a pale complexion. His face was wise, whimsical, with dark and hardened eyes that expressed a deal of pain, and a neat, black, goatee flecked with streaks of white. (PROSE: Scream of the Shalka; PROSE: Sometime Never...)

Behind the flesh-like material he was constructed of lied a silver android with golden lenses below the eyes and a speaker below his mouth, which could be revealed at the press of a button. (WC: Scream of the Shalka)

Clothing
He wore an ebony black suit whose gold buttons fastened at the collar, with dark trousers. Occasionally, he took to wear black gloves. (WC: Scream of the Shalka)

Behind the scenes

 * Derek Jacobi, who voiced the "Android Master", would go on to play a new version of in TV: Utopia, and later star in his own audio series, The War Master.
 * In his intended backstory, the Master came to the assistance of the Ninth Doctor when Gallifrey was invaded by an unknown alien race. While the other Time Lord retreated to the Matrix, the Doctor and the Master "sent the aliens packing", destroying the Master's final form in the process, causing the Doctor to construct an android body confined to his TARDIS. The Time Lords then used their power to "send the Doctor off to solve the most dangerous problems in the universe", with the Master along for the ride. (DWM 464)
 * With the Eighth Doctor Adventures being an ongoing series at the time of Scream of the Shalka's release, range editor Justin Richards connected the Eighth Doctor's continuity to that of the "Shalka" Doctor's via the Master. As Richards confirmed in DWM 338, the novel Sometime Never... tied in to Scream of the Shalka with a scene in "the room in the TARDIS where the Doctor never goes," wherein the Eighth Doctor encounters the Master's essence trapped in the Doctor's TARDIS since TV: Doctor Who. The link between the 'ghost and the machine' and the 'Android Master' was later clarified by PROSE: A Brief History of Time Lords, which stated that "some rumours" said that after the events of TV: Doctor Who "[the Master] remained trapped in the Doctor's TARDIS, his mental resources transferred into an android, acting as the Doctor's companion or pet."
 * According to the production information text on the Scream of the Shalka DVD, in original drafts of the script, instead of an android of the Master being the TARDIS Defence System, it was going to be a hologram of the Fifth Doctor. This was later changed so that it would be the Master instead.

Мастер (Крик Шалки)