The Master

“You do not understand hatred as I understand it. Only hate keeps me alive. Why else should I endure this pain?”
—The Master
**"The Master"** — known in female form as **"Missy"**, short for **"Mistress"**, and at times by various other aliases — was a renegade Time Lord, serving as both a friend and an opponent of the Doctor.

Though they had been friends from childhood and schoolmates at Prydon Academy, the Master's lust for power would eventually pull the two apart. While the Doctor and the Master would remain close friends despite their rivalry, the Master developed an intense hatred for and often sought to kill the Doctor. Despite this enmity, however, the two would on occasion act as allies.

Like the Doctor, the Master would also flee from Gallifrey in a TARDIS of his own, and fully embrace his darker nature after escaping a black hole he had been trapped in by the Second Doctor. The Master then went on to fight various battles against the Third Doctor and UNIT during the Doctor's exile on Earth, even spending a short period also trapped on the planet after his dematerialisation circuit was briefly stolen by the Doctor and when he was imprisoned on Fortress Islandafter being arrested by UNIT, until he was able to orchestrate his escape with the aid of the Sea Devils.

Following an incident that resulted in his body being badly disfigured, the Master began searching for a way to restore his Time Lord body, with only his intense hatred and burning anger keeping him alive. After spending years on Trakenmanipulating events to gain the powers of the Sourcethrough the Keeper of Traken, the Master was able to regenerate into a new body after possessing Consul Tremas, and resumed his crusade to conquer the universe and kill the Doctor.

Eventually landing on the Cheetah World, the Master became infected with the Cheetah virus, which increased his aggressive behavior. According to some accounts, the Master would continue to be plagued by the virus for some time until he overcame the effects and was either taken prisoner by his enemies, or was regressed back to his cadaverous form by the Warp Core. Another account claimed that, immediately following his escape from the Cheetah World, he was cured by Tzun nanites and regenerated after being shot by Ace.

After being sentenced to death on Skaro, the Master was able to survive his execution using a Deathworm Morphant, and would continue to survive by possessing various bodies, until he was killed by the Ravenous. However, the Master was swiftly resurrected by his other incarnations on the instructions of the Time Lords in preparation for a potential war with the Daleks.

After working with the War Doctor in the body of a child during the Last Great Time War, the Master regenerated into an older body that tried to manipulate the conflict to suit his own goals. However, after his failure to properly use the Heavenly Paradigm, the Master was driven to such a state of terror that he fled to the end of the universe and turned himself into a human baby with a Chameleon Arch to escape the Time Lords and wait out the conflict. After spending many years living as a humble human scientist on Malcassairo, the Master's personality was reawakened by Martha Jones, and he made to steal the Doctor's TARDISfrom the Tenth Doctor, but was fatally shot by Chantho and forced to regenerate into a younger body.

Using the alias "Harold Saxon", the Master engineered his election as Prime Minister of the United Kingdom in the 2008elections, and then sought to use the Earth to create a new Gallifrey. When his plan was foiled, he was shot by his wife, Lucy, and decided not to regenerate and die to spite the Doctor. Following a faulty resurrection by the Disciples of Saxon, the Master used the Immortality Gate to create the Master Race and attempted to free Gallifrey from the Time lock of the Last Great Time War, but instead entered the last day of the war to get revenge on Rassilon.

After Gallifrey returned to the universe, the Master left, and eventually ended up on a Mondasian colony ship, where he came face to face with a future female incarnation of himself, who stabbed him to ensure his regeneration into her. Now female, the Master began to call herself Missy, the self-proclaimed "Queen of Evil". She embarked on a scheme to rekindle her friendship with the Doctor, believing she could convince him they were the same by offering him the power to end tyranny with an army of Cybermen, but the Doctor refused to submit to the temptation.

Eventually, Missy was captured and imprisoned inside a Quantum Fold Chamber which was moved into a vault at St Luke's University by the Twelfth Doctor and Nardole. Although she claimed she could leave the Vault anytime she wanted to, she chose not to because she wanted to become good. So the Doctor tried to rehabilitate her and rekindle their friendship on his terms. Just as she was about to make a breakthrough, Missy joined with her previous incarnation, only to then betray and kill him to join the Doctor, but was killed herself before she could.

Despite this, the Master returned again in a new body. He 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. He next turned to plague the Thirteenth Doctor and Team TARDIS, eventually revealing the truth about the Timeless Child and building 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.