Like the Doctor, the renegade formerly known as Koschei or Magnus has employed a number of aliases in the course of his career. However, while the Doctor tends to use false names on a fairly ad hoc basis in order to avoid awkward questions, the Master usually adopts them in order to further whatever scheme he is currently embarked upon.
Variations on 'the Master'
The Master
The Master has effectively discarded his former name. He and the Doctor refer to each other by their titles as a matter of course.
The War Chief
The novel Time's Champion indicates that an early incarnation of the Master was the War Chief , who under this alias with the War Lords in an effort to take over the galaxy using human soliders from various wars in Earth's history. This plot was thwarted by the Second Doctor. (DW: The War Games)
Colonel Masters
Used when infiltrating Rex Farrell's plastics company. (DW: Terror of the Autons)
Reverend Magister
Used when infiltrating Devil's End. Magister is Latin for Master. (DW: The Daemons)
Professor Thascales
Used when infiltrating the Newton Institute. Thascales is Greek for Master. (DW: The Time Monster)
'Duke' Dominus
Used when impersonating a gangster in 1930s Chicago. Dominus is also Latin for Master. (ST: The Duke of Dominoes)
Estro
Used when posing as an adviser to Lord Haldoran in post-Dalek invaded Earth in 2299, in an effort to procure a Dalek matter-transmuter.
Sir Gilles Estram
Used when attempting to avert the signing of the Magna Carta. Estram is an anagram of Master. (DW: The King's Demons)
Mr. Seta
Used aboard the starship Gallery. Another anagram of Master. (BFA: Dust Breeding)
Mr. Harold Saxon
Mister Saxon is an anagram of "Master No Six" - implying the sixth form of the Master seen on screen. Used as a human name to become Prime Minister in 2008. After establishing contact between Humanity and the Toclafane, he revealed himself and commanded the Toclafane to "Decimate" (kill one tenth of) humanity. (DW: The Sound of Drums)
Other Aliases
Dr Emil Keller
Used when assuming the identity of the creator of the Keller Machine. (DW: The Mind of Evil)
- In an alternate timeline the Master used this identity when working for the government of China, during which time he was known as Ke Le. (DWU: Sympathy for the Devil.)
The Adjudicator (Martin Jurgens)
Used when impersonating an Adjudicator (strangely enough). (DW: Colony in Space)
The Keeper of Traken
More of a job title than an alias, but for a short time the Master was the Keeper. (DW: The Keeper of Traken)
The Portreeve
Used when attempting to trap the Doctor in Castrovalva. (DW: Castrovalva)
Kalid
Used when attempting to take control of the Xeraphin gestalt, this is the only time his choice to take on an alias is not explained or has a good reason. (DW: Time-Flight)
The Sheriff
Used when trying to gain access to the regenerative fountain near Eternity. (ST: A Town Called Eternity)
Godspodar
Used when attempting to access the TITAN array in order to destroy the Chronovores. (PDA: The Quantum Archangel)
Major Kreer
Used when allied with the Tzun in 1950s America. (NA: First Frontier)
Doctor John Smith
Used while living as an amnesiac on an un-named colony world. The Doctor also frequently used this alias. (BFA: Master)
Bruce
The name of the paramedic whose body the Master possessed in San Francisco in 1999. The Master assumed his identity on a number of occasions during this affair. (DW: Doctor Who: The TV Movie)
Professor Yana
Used while living as a human at the end of the Universe. He had used a Chameleon Arch to make himself human to escape the Last Great Time War; the name is an acronym of the Face of Boe's final words: "You Are Not Alone". (DW: Utopia)
For more information see Professor Yana
Mr Saxon
Mr. Harold Saxon (DW: The Lazarus Experiment) was a politician on Earth. He was active from at least April 2007 when he started campaigning for the general election (DW: Love & Monsters) and was elected Prime Minister in 2008 (DW: The Sound of Drums / Last of the Time Lords). He took his campaign seriously, placing posters on walls across Great Britain. (TW: Captain Jack Harkness, DW: Smith and Jones)
He claimed that extraterrestrial life did exist, making him more popular in early 2008 after reports from the Royal Hope Hospital about the Judoon on the Moon (DW: Smith and Jones). Earlier, he also ordered the destruction of the Racnoss Webstar on Christmas Eve 2007. (DW: The Runaway Bride) It was also at this point that he revealed himself as the Master. Defeated by the Doctor using telekinesis gained from the psychic energy of everyone on Earth and shot and killed by his wife and companion Lucy Saxon. Refuses to regenerate and dies for good... perhaps.