Fourth Doctor

Independence
Having regenerated, the Fourth Doctor seemed to be in a hurry to leave Earth, but was eventually persuaded to stay and help Brigadier Lethbridge-Stewart deal with Think Tank and their K1 robot. The Fourth Doctor took Sarah Jane Smith and Harry Sullivan to travel with him in the TARDIS. (DW: Robot)

In the midst of another adventure, a Time Lord appeared to the Doctor and offered him a mission, to intervene in the creation of the Daleks, either to prevent it, or to induce the Daleks to develop into less dangerous creatures. (DW: Genesis of the Daleks)


 * This set into motion a series of events that would eventually lead to open war between Daleks and Time Lords and the destruction of Gallifrey.

Upon his return to Earth and the defeat of the Zygons, Harry decided to remain. (DW: Terror of the Zygons)


 * ''The Doctor had begun, even more so with this regeneration, to break his ties with Earth. We do not know when, if ever, he formally left his position as UNIT's unpaid scientific advisor or if he had not done so already.

Return to Gallifrey
After many adventures together, the Doctor received a telepathic summons from Gallifrey and returned Sarah to Earth (DW: The Hand of Fear), though mistakenly, not to her home in South Croydon but to Aberdeen. (DW: School Reunion).

On Gallifrey, the Doctor defeated the Master and renewed his acquaintance with his former teacher Borusa. He also re-experienced, to his disgust, the decadence of Time Lord civilization. (DW: The Deadly Assassin).


 * The Doctor travelled for an unknown period of time alone.

New friends
Visiting a nameless jungle world, he made the acquaintance of Leela of the Sevateem (DW:The Face of Evil)

Lord President of Gallifrey
Returning once more to Gallifrey and, posing as vainglorious and power-mad, sought and attained the office for Lord President as part of a scheme to save his home world from an invasion force of two separate enemies, the Vardans and the Sontarans. Leela decided to remain on Gallifrey with Andred, a Gallifreyan in the Chancellory Guard and K-9. However, the Doctor left the Capitol with a duplicate K-9, Mark II, in a crate (DW: The Invasion of Time).


 * The Doctor and K-9 Mark II spent an indeterminate period of time together.

Quest for the Key to Time
The White Guardian summoned the Doctor to initiate a quest to locate and assemble the segments of the Key to Time. For this purpose, the White Guardian introduced him to a new companion, Romana (DW: The Ribos Operation).The Doctor and Romana located, assembled and disassembled the Key, and to escape the wrath of the White Guardian's opposite, the Black Guardian, the Doctor installed a randomiser in the TARDIS console (DW: The Armageddon Factor).

E-Space
Struggling with the Master, he fell off the Pharos Project radio telescope down to the ground hundreds of feet below. The mysterious entity known as The Watcher, which had been tracking him through time and space, then merged with him and he regenerated.



Appearance
In stark contrast to the elegant, refined figure of his third incarnation, the Doctor was an unkempt, awkward-looking figure, dressed in battered clothing and an impossibly long multi-coloured scarf, knit for him by Madame Nostradamus. (DW: Robot). His dark curly hair was often partially hidden by a large floppy hat.

Personality
This incarnation was most definitely not Human, and stood apart from others, even most of his own people. (DW: The Deadly Assassin, The Invasion of Time)

When Sarah upbraided him over his callousness at the sight of a man killed by the animate corpse of his own brother, the Doctor reminded her of the larger issue of stopping Sutekh. (DW: Pyramids of Mars). His mind five leaps ahead of anyone, including himself, only Romana seemed able to keep up with the Doctor's trains of thought. He delighted in keeping both friends and foes alike off guard with oddball humour and curious pranks, as in his second incarnation.

He could judge character keenly almost instantly whether knowing who to trust or seeing through Unstoffe's faux guilelessness (DW: The Ribos Operation). Out of all the Doctor's selves, this incarnation had perhaps the most consistently anti-authoritarian attitude, having little tolerance for religious dogma (DW: The Brain of Morbius, Underworld) or nationalism (DW: Robot, The Armageddon Factor). The Doctor often played the fool to lull his opponents, such as Count Scarlioni, into underestimating him (though it did not work in that case.) But he was also a very intense, brooding individual, at times displaying a seriousness and fury belying his usually whimsical attitude, such as when telling the scientist Sorenson that he must put right what he done wrong, even if he must sacrifice his life to do so (DW: Planet of Evil).

In Destiny of the Doctors, the Master called this Doctor 'the Bohemian, the wanderer; one so keen to abandon his roots that he abandoned his sense!'

Habits and Quirks
Souvenirs from many different worlds littered his pockets. (DW: Robot, Genesis of the Daleks). He would sometimes relax by playing with a yo-yo and liked to drink ginger beer (DW: The Android Invasion).

He would often have with him and offer jelly babies as a greeting. In his later life he developed a great reliance for tinkering about in the TARDIS. He relied upon his sonic screwdriver at least as much as in his previous incarnation.

Unrecorded adventures

 * Presumably by himself, the Doctor visited Leela's home planet, encountered the supercomputer Xoanon and inadvertently installed in him a program copied from his own personality (DW: The Face of Evil).


 * ''We do not know at what time in the Fourth Doctor's life this event could have occurred or the reason why, later, he would fail to remember his adventure. One theory for the amnesia explains that this adventure as happening very early in his life, when he still suffered from post-regenerative trauma.


 * In the first episode of the fourth Doctor, Robot, he is delirious from his regeneration and placed in a UNIT sickbay. He escapes in the TARDIS, appearing to abandon Sarah Jane on Earth. He then returns, a little more stable.


 * In the episode The Face of Evil, when the Doctor discovers that Xoanon is a product of his tampering, he mentions that he had just regenerated and was confused (thus the excuse for why the computer was schizophrenic). It is likely that his tampering occurred when he left in the TARDIS in Robot.

Key Life Events

 * The Doctor regenerates. (DW: Planet of the Spiders, Robot)
 * Gains a new companion in Harry Sullivan and drives Bessie for the last time until his seventh incarnation. (DW: Robot)
 * The Doctor tries to prevent the creation of the Daleks and first encounters Davros. (DW: Genesis of the Daleks).
 * The Doctor and the Brigadier work together for the last time before the Brigadier's retirement. (DW: Terror of the Zygons). Soon after, he discontinues his active involvement with UNIT (DW: The Android Invasion and DW: The Seeds of Doom)
 * Harry Sullivan departs and returns to UNIT (DW: Terror of the Zygons) though he briefly reunites with the Doctor soon after (DW: The Android Invasion).
 * Sarah Jane Smith leaves (DW: The Hand of Fear) and the Doctor returns to Gallifrey, where he defeats the Master (DW: The Deadly Assassin). Afterwards, he travels alone for a time.
 * Gains a new companion in Leela and sets out to be Professor Henry Higgins to her Eliza Doolittle (DW: The Face of Evil).
 * Obtains his first robotic companion, K-9. (DW: The Invisible Enemy).
 * The Doctor assumes the office of Lord President on Gallifrey, fights back two invasions. Afterwards, Leela and K-9 choose to stay on Gallifrey; the Doctor begins assembling a second K-9. (DW: The Invasion of Time)
 * The White Guardian puts the Doctor on his quest to find the Key to Time and introduces him to future Lady President Romana, who is assigned to him as a new companion. (DW: The Ribos Operation) Once defeated, the Black Guardian swears revenge. (DW: The Armageddon Factor).
 * The Doctor temporarily instslls a randomizer into the TARDIS, intentionally making the vehicle's travels unpredictable. (DW: The Armageddon Factor)
 * Romana chooses to stay with the Doctor rather than return to Gallifrey, and regenerates into a new body. (DW: Destiny of the Daleks)
 * En route to Gallifrey (due to Romana being summoned back against her will), the TARDIS crew find themselves in E-Space where they find a new companion, Adric (DW: Full Circle).
 * Romana and K-9 leave the Doctor before he returns to N-Space. (DW: Warriors' Gate)
 * After gaining two new companions, Nyssa and Tegan Jovanka, the Doctor regenerates while saving the universe from a new incarnation of the Master. (DW: Logopolis)