The Master (Terror of the Autons)

The thirteenth incarnation of the Time Lord known as the Master was a renegade, seen by his own people as one of their worst members. Though initially friends with him, the Master had, by this time, already sworn enmity against the Doctor. (DW: Terror of the Autons)

For much of his life, he opposed the Third Doctor and UNIT, mainly in the late 20th century in England, though occasionally in other times and places. He eventually became trapped there and was even imprisoned at one point. (DW: The Mind of Evil, The Sea Devils)

As this was his thirteenth body, the Master began to decay as his body fell into ruin. He devoted his time to finding a means by which he could rejuvenate himself, and eventually did so. (DW: The Deadly Assassin, The Keeper of Traken)

However this is probably not his thirteenth body and he could have used more between delgados last adventure and the deadly assassin as he never mentioned this was his last body.

Preparations
Before the Third Doctor became aware of his presence, the Master had infact been on Earth for some time.

The Master was present at the first Auton invasion of Earth. He had apparently seen or heard about Channing attempt to capture the Third Doctor. He contacted journalist James Stevens by phone, who's article he had read in the Daily Chronicle, and told him about the near-kidnapping. (MA: Who Killed Kennedy, DW: Spearhead from Space)

He later called Stevens again, during the Silurian attacks on Wenley Moor. He informed Stevens that Frederick Masters had been the first to have died from the plague sweeping London. (MA: Who Killed Kennedy, DW: Doctor Who and the Silurians)

Shorty after the Inferno Project incident, the Master once more contacted James Stevens, this time to check up on his work on his U.N.I.T. article. He promptly hang up when Stevens mentioned C19 and Glasshouse. (MA: Who Killed Kennedy)

He first infiltrated the headquarters of UNIT while the Brigadier and the Doctor had gone to meet with government officials. He hypnotised the Doctor's assistant Liz Shaw and, through her, learned of recent events, including the recent failed Nestene invasion and the awakening of the Silurians. This inspired him to ally himself with them and to locate any more Silurian colonies. (DWY: Reconnaissance)


 * The Master appears to have originally intended to proceed directly with his plan to use the Keller Machine, as he spent many months establishing his (and the Keller Process') credentials, and must have brought the mind parasite to Earth with him prior to joining forces with the Nestenes.

At some point, the Master also stole Time Lord files on matters including the Doomsday Weapon. (DW: Colony in Space) This may have taken place before or after his encounters with the Third Doctor on Earth.

Encounters with the Doctor
The Master had already appeared at a circus, his TARDIS in the form of a circus trailer or horse box. He hypnotised the circus troupe to obey his orders as part of his plan to assist the Nestenes in their latest bid to conquer Earth. A Time Lord emissary alerted the Doctor to his rival's presence on the planet. After the failure of the Master's plan, he fled. (DW: Terror of the Autons)

The Doctor stole the dematerialisation circuit of the Master's ship, stranding him on Earth. He returned again, posing as the scientist who had "developed" the Keller Machine, in reality a living alien entity. He used prisoners as a plan to hijack a missile containing nerve gas and use it cause a conflict that would trigger a nuclear war. (DW: The Mind of Evil)

The Master recovered the functioning of his TARDIS and brought Axos to Earth hoping to ally himself with them. Instead he became the prisoner of Axos and only escaped with the aid of CIA agent Bill Filer. The Doctor tricked the Master into thinking he was going to betray Earth. Instead, he trapped the Master with Axos in a time loop. (DW: The Claws of Axos)

Posing as an Adjudicator, the Master then visited a human colony on the planet Uxarieus in the year 2472. The stolen Time Lords' records had informed him that here he would find the Doomsday Weapon created by a near-extinct native species. The Doctor once more defeated him. (DW: Colony in Space)

The imprisonment of the Master
In the Wiltshire village of Devil's End, he summoned the Dæmon Azal. At the conclusion of this event, UNIT captured him. (DW: The Dæmons) Following a trial by human authorities, the Master was sentenced to life imprisonment in a prison on an island designed especially to hold him. (DW: The Sea Devils) The government used him as a scapegoat for all the alien attacks that had occurred. (MA: Who Killed Kennedy)

While in custody, with the Doctor gone to Peladon, (DW: The Curse of Peladon) the Master collaborated with UNIT to prevent an invasion by a fascist version of Earth. (PDA: The Face of the Enemy) The Master quickly gained control over his jailer, George Trenchard, and nearly caused a war between humans and Sea Devils, a species related to the Silurians. He later escaped in the confusion. (DW: The Sea Devils)

Events following the Master's escape
Some time during his obvious actions against the Doctor and UNIT, the Master infiltrated the government's Department C19 to a shocking degree. He took control of the Glasshouse, a facility for traumatised UNIT soldiers, and in particular Francis Cleary. He also tried to undermine UNIT in the short term. In the long term, he planned to use a time ring to have Cleary go to 1963 to prevent the Kennedy assassination, thereby altering Earth's history to make it more vulnerable to invasion. The plan failed. (MA: Who Killed Kennedy)

The Master travelled to ancient Atlantis and, confronting the Doctor there, brought forth Kronos, king of the Chronovores. Kronos captured him but allowed him to go free. (DW: The Time Monster) Returning to 1970s Earth, he used time-displaced Scottish warriors to seize a nuclear submarine and threaten Britain with obliteration if he wasn't given the Doctor's TARDIS; he ended up temporarily trapped in the 18th century. (TVC: The Glen of Sleeping) He also worked with the Gaderene race to conquer Earth. (PDA: Last of the Gaderene)

He forged a short-lived alliance with the Daleks, acting as their agent to provoke warfare between the Earth Empire and the Draconian Empire in the 26th century. To achieve this, he employed a force of Ogrons who, through the use of hypnosound, made themselves appear human or Draconion, thus provoking the other side. When the Doctor revealed the true perpetrators, the plot was abandoned. (DW: Frontier in Space)

For a short while the Master adopted the identity of Duke Dominus, a gangster on early 20th century Earth, but his plan on this occasion was halted by the Fourth Doctor without the Master even knowing it. (VD: The Duke of Dominoes)

The Master finally went under cover on Earth following the 22nd century Dalek invasion and killed David Campbell, the husband of the Doctor's granddaughter Susan. After being defeated by the Eighth Doctor, he degenerated when exposed to a lethal blast from a Dalek artefact, caused by Susan Foreman. (EDA: Legacy of the Daleks)

Escape to Tersurus
When the Time Lord Chancellor Goth came to Tersurus to investigate the materialisation of an unauthorised TARDIS, (EDA: Legacy of the Daleks) he found the Master in a wasted condition, that of a decaying animated corpse. (DW: The Deadly Assassin)

On Gallifrey
The Master made Goth, in line for the position of Lord President of the High Council of Time Lords, into his slave. He also took over the mind of Solis, one of the Chancellory Guard. With a telepathic summons and a vision of the future created by the Matrix, the Master lured the Fourth Doctor to Gallifrey to prevent the murder of the then-serving Lord President. The Doctor failed and ended up on trial for the President's murder. In the mean time, the Master casually killed a guard with his Tissue Compression Eliminator and left it for the Doctor to find like a grisly calling card.

Secretly, the Master had access to the Matrix. He also had guessed the secret of the Eye of Harmony and various artefacts left behind by Rassilon. He realised that the Eye of Harmony, a black hole, resided beneath the Panopticon and, realising that it had immense power, believed he could use the Sash of Rassilon to protect himself from the raw power of the Eye and the destruction that unleashing it would cause. He thought that it could channel that energy to renew himself.

The Doctor defeated the Master in physical combat and he appeared to have fallen into a crevice created by a localised earthquake. In fact, he had gained access to his TARDIS, disguised as a grandfather clock, and escaped. (DW: The Deadly Assassin)

On Traken
The Master travelled to the planet Traken, the centre of the Traken Union, in a TARDIS configured into the sculpture-shaped Melkur. He set about a plan to steal the Source to restore himself. To this end, over a period of years, he won over Kassia, who later married Tremas and became a stepmother to Nyssa. Defeated once more by the Fourth Doctor and Adric, he took over the body of Tremas. (DW: The Keeper of Traken)

Personality
This incarnation of the Master was suave and debonair with a sardonic sense of humour. A haughty psychopath, he regarded most beings as his inferiors but had a mutual respect for the Doctor as a worthy opponent and (almost) his intellectual equal. (DW: The Sea Devils)

While in Atlantis, the Master formed something of a relationship with Queen Galleia, remarking that she was beautiful, and promising her power. Both she and Lakis commented that he had "the bearing of a God". (DW: The Time Monster)

Following his degeneration, he became less charming and witty. He was mainly preoccupied with finding a way to regenerate. The vengeful and vindictive side of the Master was at its most apparent while he was in this state. (DW: The Deadly Assassin, The Keeper of Traken)

Behind the scenes

 * Although they played antagonists onscreen, in real life Roger Delgado (the Master) and Jon Pertwee (Third Doctor) were actually close friends. In interviews and convention Q&A sessions, Pertwee often cited the death of Delgado as one of the factors which led him to give up the role.