CyberMaster

The CyberMasters were a race of Cybermen created by from the corpses of the Time Lords who had been on Gallifrey when he destroyed the Capitol, claiming them all to have been "born" from the Doctor.

Characteristics
The CyberMasters possessed Cyber-bodies very similar to those of the Cyber-Warriors that Ashad reawakened in the aftermath of the Cyber-Wars of the Cyberium, though they possessed several notable differences.

The Cyber-helmets of CyberMasters had large, silver Time Lord headdresses, with Gallifreyan symbols on the sides and the outer layer of their faceplates, in place of a pair of side handles. The CyberMasters' faceplates also featured "tear-drop" eye-pods that angled vertically, rather than diagonally, and their mouth slits were grated frowns rather than a solid line. Each CyberMaster wore a long, black robe with Gallifreyan symbols etched down the inner front sleeves. (TV: The Timeless Children)

The CyberMasters were modified into a hierarchy by the Master's Dalek Plan. Later models had a conventional mouth slit on the faceplate. The Cyber-Leader was one of only two that wore a cape and headdress, distinguished by its silver headdress whilst its subordinate's was black. Other CyberMasters sported helmets with conventional side handles, but retained Gallifreyan writing on their bodies. (TV: The Power of the Doctor)

The voices of CyberMasters were highly reminiscent of the voices of the early Cybermen of Cybus Industries. (TV: Rise of the Cybermen, The Age of Steel) The CyberMasters possessed Cyber wrist blasters identical to those of the Cyber-Warriors they were based upon; several dozen blasts from these wrist blasters could mortally injure a human, with the injuries sustained leading to death within a second.

The most striking characteristic of the CyberMasters was their ability to regenerate; converted these Cybermen from the corpses of Time Lords and genetically spliced the Time Lords' regenerative abilities into them. This effectively gave the CyberMasters an advanced self-repair system, allowing them to regenerate and recover from otherwise-fatal damage. The Master proclaimed that this made the CyberMasters "invincible", and demonstrated to the Thirteenth Doctor the CyberMasters' regenerative powers by having one CyberMaster shoot another CyberMaster with its Cyber wrist blaster; the latter CyberMaster was temporarily terminated, but quickly regenerated and fully restored itself. However, as they contained organic components, the CyberMasters were still vulnerable to the death particle, even after it had been shrunk by the Master's Tissue Compression Eliminator. (TV: The Timeless Children) Their regeneration energy being used to power a retro-regeneration for the Doctor drained their regenerative powers completely, leaving the CyberMasters permanently dead. (TV: The Power of the Doctor)

As shown by one individual, the Cyber-Leader rank existed amongst the CyberMasters. (TV: The Power of the Doctor) Anomalously, although the CyberMasters, being a Cyber-subspecies, were programmed to be emotionless, they would not immediately obey an order if it would result in damage to a fellow CyberMaster; indeed, when the Master demonstrated the CyberMasters' regenerative capabilities to the Doctor, the CyberMaster he ordered to shoot at a fellow CyberMaster was initially reluctant to do so, until the Master angrily ordered it to comply. (TV: The Timeless Children)

Prelude
The Master had previously created two branches of Cybermen in earlier incarnations. As, he manipulated the people of a Mondasian colony ship into being converted into CyberMondans. (TV: World Enough and Time, The Doctor Falls) His next incarnation, Missy, would later create an army of what she called "Cyberdears" in an plot to tempt the Twelfth Doctor. (TV: Death in Heaven) One account also holds that Rassilon had once led the last Cybermen in the universe in a plot of vengeance against the Time Lords that the Cybermen used as an opportunity to try to convert the Time Lords, and all of time and space. This plot was undone by the Twelfth Doctor, erasing this attempted conversion from existence. (COMIC: Supremacy of the Cybermen)

At some point onboard a Cyberman-controlled ship, while looking for River Song, the Twelfth Doctor told Missy they had to be careful if they didn’t want to end up turned into Cybermen too. Missy replied that the idea of Cyber Time Lords had potential. (GAME: Lost in Time)

When the Spy Master hacked into the Matrix on Gallifrey, he accidentally discovered the story of the Timeless Child; furious that the entirety of Time Lord civilisation had been built on "a lie", the Master destroyed the Capitol and committed genocide against the Time Lords. (TV: Spyfall) However, he chose to preserve the corpses of the Time Lords, believing them to be of use someday. (TV: The Timeless Children)

Sometime after escaping the Kasaavin realm, (TV: Spyfall, Fugitive of the Judoon) the Master passed through the Boundary when it opened between its planet and Gallifrey, (TV: Ascension of the Cybermen) and took the Thirteenth Doctor back to the ruins of the Citadel. While the Doctor was trapped within the Matrix, the Master welcomed Ashad to pilot his Cybercarrier to Gallifrey. Inside the heart of the Capitol, the Master, disappointed by Ashad's plan to transform the Cybermen into a purely robotic species and then use the death particle to destroy all organic life, persuaded Ashad into an alliance with him, claiming that doing so would make the Cybermen the true dominant species of N-Space. (TV: The Timeless Children)

Creation of the CyberMasters
Onboard the Cybercarrier, the Master killed Ashad and absorbed the Cyberium after it left Ashad's corpse; with their combined knowledge of the Cybermen's entire history and the Matrix, the Master and the Cyberium converted the Time Lord corpses frozen in stasis by the Master into the CyberMasters, before returning to the heart of the Capitol. Inside the heart of the Capitol, the Master awoke the Doctor and unveiled twelve of the CyberMasters to her. In addition, he ordered one CyberMaster to shoot another, demonstrating the CyberMasters' regenerative abilities. Declaring the CyberMasters to have been "born" from the Doctor, and that their creation was "a new era dawning", the Master and the CyberMasters departed. The CyberMasters and the Master were later confronted in the heart of the Capitol again by the Doctor, after she broke out of the Matrix and found Ashad's shrunken corpse onboard the Cybercarrier.

The CyberMasters attempted to shoot the Doctor on sight, but were called off by the Master. Armed with one of Ko Sharmus' explosives, with Ashad's miniaturised corpse attached, the Doctor attempted to detonate the explosive and, by extension, the death particle within Ashad's corpse, to destroy the CyberMasters, along with herself and the Master. However, after failing to detonate the bomb out of hesitancy, Ko Sharmus arrived, having chosen not to escape in the spare TARDIS used by the rest of Team TARDIS, Ravio, Yedlarmi and Ethan. (TV: The Timeless Children) Revealing that he had been part of the Alliance, (TV: Fugitive of the Judoon) who had sent the Cyberium to Earth in 1816, (TV: The Haunting of Villa Diodati) Ko Sharmus persuaded the Doctor into letting him detonate the death particle while she escaped in another TARDIS. Enraged, the Master ordered the CyberMasters to kill Ko Sharmus; despite being shot dozens of times in only a few seconds, Ko Sharmus detonated the explosive, thereby detonating the death particle. The Master ordered the CyberMasters to escape with him, immediately before the death particle exploded. (TV: The Timeless Children) However, both the Master and his CyberMasters survived. (TV: The Power of the Doctor)

Return and Demise
The CyberMasters later resurfaced as part of the Master's Dalek Plan, where they were allied with both the normal Cybermen and the Daleks. The CyberMasters, led by a Cyber-Leader attacked a space-faring bullet train to capture a Qurunx. While they were defeated by the Doctor, Yasmin Khan and Dan Lewis, they still managed to succcessfully capture the Qurunx. After the Master stole the Doctor's body and identity, an AI hologram of the Fugitive Doctor tricked the CyberMasters into shooting each other, allowing Yasmin Khan and Inston-Vee Vinder to overpower the Master before the CyberMasters began to regenerate. On the hologram's direction, Yaz channelled all of the CyberMasters' regeneration energy into the Doctor's body, powering a retro-regeneration that restored the Doctor back to herself and sent the Master back into his original body. This appeared to drain the CyberMasters of their regenerative capability completely, leaving them permanently dead. After awakening, the weakened Master abandoned his CyberMasters as he went after the Doctor. (TV: The Power of the Doctor)