Fourth Doctor (Earth-12)

The Fourth Doctor was the seventeenth incarnation of the Time Lord known as Sir Loki the Other and the fourth incarnation of his rebirthed body that was born to the House of Lungbarrow.

He left all ties of his previous incarnation's exile behind on Earth, setting off to travel the cosmos. He initially travelled with Sarah Jane Smith and Harry Sullivan, but Harry chose to remain on Earth when the opportunity arose. The Doctor and Sarah Jame continued on their adventures until the Doctor was summoned to Gallifrey, necessitating that he leave Sarah Jane behind as humans were not allowed on Gallifrey at that time.

After leaving Gallifrey, he met and travelled with Leela of the Sevateem. During his travels with Leela, the Doctor gained a new companion in the robot dog, K9. Returning once more to Gallifrey to stop an invasion, Leela and the original K9 stayed behind there. On the White Guardian's orders, the Doctor began looking for the Key to Time with fellow Time Lord Romana and K9 Mark II. Once that search was concluded, the Doctor and a newly-regenerated Romana went on the run from the Black Guardian. They accidentally passed into the smaller Universe of E-Space.

During his travels in E-Space, the Doctor gained a new companion in the young mathematical genius Adric. Romana and K9 stayed behind in E-Space as the Doctor and Adric departed for N-Space.

Once again encountering his old enemy the Master, the Doctor and Adric met a Traken girl named Nyssa. She would later join them, along with the human Tegan, to help him prevent the destruction of the Universe by entropy. While stopping the Master from using this threat to blackmail the Universe into servitude, the Doctor fell from the Pharos Project telescope and regenerated for the fourth time.

Foreshadowing
The Third Doctor first regenerated after he fell off a roof during a struggle. However, the Nurazh attempted to take over the Doctor's mind, but, unable to cope with two Time Lord minds at the same time, perished, thus healing the Doctor back to his third incarnation. Jo Grant saw the Fourth Doctor long enough to describe him to the Third Doctor. (ST: The Touch of the Nurazh)

Post-Regeneration
The Doctor's third incarnation regenerated some time after the radiation from the Great One's lair took effect upon him. He returned to Earth to end his time in the company of Sarah Jane and the Brigadier after being lost in the Time Vortex. K'anpo Rimpoche arrived and gave the Doctor a push for his regeneration, which he warned would scramble his mind. (DW: Planet of the Spiders)


 * "Typical Sontaran attitude... stop Linx... perverting the course of human history... I tell you Brigadier, there's nothing to worry about. The Brontosaurus is large and placid..."

- First Words of the Fourth Doctor

Once he had regenerated, the Doctor suffered delirium, mumbling random things from his adventures, and was physically exhausted. He was put in sickbay, where Harry Sullivan kept watch on him. However, the Doctor managed to outwit him and get to the TARDIS to choose his new wardrobe. Though he still had a hard time realizing things around him, the Doctor was asked by the Brigadier to help deal with Think Tank and their K1 robot, which had gone insane from so many contradictory orders its programming should have prevented it from doing. Afterwards, he took Sarah Jane Smith and Harry Sullivan to travel with him in the TARDIS, unofficially abandoning his laboratory and UNIT membership. (DW: Robot)

However, despite intending to resign from UNIT, (DW: Pyramids of Mars) the Doctor never formally left his position as their unpaid scientific adviser; (DW: The Sontaran Stratagem) other scientists had to be hired to take his place during his absence. (DW: Planet of the Dead)

Adventures with Sarah Jane and Harry
The Doctor's first trip with his companions was an accidental one due to Harry messing around with the console controls. The TARDIS landed on Space Station Nerva, where humanity had been cryogenically suspended to await Earth's recovery from solar flares. However, the Wirrn posed a threat as they wished to use the humans as food and incubators for their kind. Luckily, Noah, a human converted in a Wirrn, retained his humanity and tricked the Wirrn into a suicide. On behalf of the space station, the Doctor went down to Earth with Harry and Sarah Jane to fix the relay. (DW: The Ark in Space)

However, once there, he found the Sontaran Styre and quickly dealt with him to ensure humanity could resettle Earth. Fixing the relay allowed the Doctor and company to return to the space station. (DW: The Sontaran Experiment)

Whilst in the midst of traveling back, a Time Lord appeared to the Doctor and offered him a mission: to intervene in the creation of the Daleks. He was either to prevent it, or to induce the Daleks to develop into less dangerous creatures. Although he was morally unable to commit genocide by destroying the entire race, he did manage to delay their advancement. (DW: Genesis of the Daleks)

After departing Skaro, the Doctor, Harry, and Sarah Jane ended up on Space Station Nerva at a time when it orbited Jupiter. While waiting for the TARDIS to catch up with them, the Doctor became involved with stopping a Cyberman attack on Voga, the planet of gold. He ultimately stopped them from blowing it up and saved Sarah Jane from the fatal bite of a Cybermat. (DW: Revenge of the Cybermen)

Upon being contacted by the Brigadier to return to Earth for assistance, something that angered the Doctor, the Doctor encountered the Zygons and helped defeat them. Though the Doctor offered him a quick lift back home, Harry decided to end his travels with the Doctor. (DW: Terror of the Zygons)

Soon after Harry's departure, the Doctor and Sarah Jane encountered anti-matter monsters before reciving a summons back to Earth. (DW: Planet of Evil)

Attempting to return to UNIT, the Doctor had to prevent the last of the Osirians, Sutekh, from escaping his prison pyramid on Mars and bringing destruction to the Universe. Though unsuccessful in stopping Sutekh's release, the Doctor was able to defeat him by ageing him for 4000 years, ageing him to death. (DW: Pyramids of Mars)

Arriving back in present day Earth, the Doctor seemingly found himself in a town Sarah Jane had previously visited, only to find it was a facsimile populated by androids under the control of the Kraals. The Kraals' own world had become uninhabitable, leading them to plan on wiping out Earth's population with a virus, then populating the planet themselves. The Doctor stopped them with the help of UNIT. (DW: The Android Invasion)

The TARDIS was next forced to land on Karn by the Time Lords to prevent the return of Morbius. The Doctor stopped the Frankenstein-esque resurrection of Morbius, but nearly died as a result. The Sisterhood of Karn used the Elixir of Life to heal him. (DW: The Brain of Morbius)

Soon after, the Doctor helped stop a Krynoid victim from taking over the Earth with plants, with the help of UNIT once again. (DW: The Seeds of Doom)

During a trip in space, the Doctor accidentally brought Helix Intelligence to San Martino in the 15th century, where it planned to dominate the human race by using the Brotherhood of Demnos as its agents. The Doctor was able to stop this by reversing the energy flow, which drained the servants of the energy they were given, killing them in the process, but saving Earth. (DW: The Masque of Mandragora)

Later, the Doctor and Sarah Jane ended up in a quarry, where an explosion nearly cost Sarah Jane her life. The Doctor found she obtained a petrified hand in the rubble and was possessed by Eldrad, who forced Sarah Jane to take it to a nuclear power station, where it regenerated into a rock-based humanoid. The Doctor complied with Eldrad's request to be taken back to Kastria, where it was revealed it went mad and caused the end of his species; it planned to rule Earth, but the Doctor managed to trip him into a pit. (DW: The Hand of Fear)

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

Return to Gallifrey
Upon return to Gallifrey, the Doctor tried to prevent the death of the Lord President, but was unsuccessful, ending up getting the blame instead for his murder. The Doctor put off execution by announcing his own candidacy for Lord President, buying him enough time to find a degenerated Master was responsible. Defeating the Master, the Doctor left his former teacher Borusa in charge. (DW: The Deadly Assassin)

Leela and K-9
The Doctor returned to the planet colonised by the Mordee centuries before, where he found that he was remembered as an evil god by the descendants of the colonists. Descendants of the colonist's survey team had become a warrior tribe called the Sevateem, while descendants of the technicians had become a technologically advanced tribe called the Tesh. After the Doctor cured the computer, one of the Sevateem, Leela, joined him on his travels. (DW: The Face of Evil)

The Doctor brought the intelligent but uneducated Leela to many locations in human history, teaching her about science and her own species' past. In Victorian London, the pair encountered the magician Li H'sen Chang and his master, the self-styled Weng-Chiang, who was actually the 51st century criminal Magnus Greel. (DW: The Talons of Weng-Chiang)

The Doctor, having become the host of the Nucleus, travelled to the Bi-Al Foundation medical centre in the year 5000, where its Swarm spread further. The Nucleus brought itself out of the Doctor's body and into the macro world to hatch more young. The Doctor travelled to Titan Base, where a hive of Swarm lay. The Doctor mixed the oxygen canisters with the methane atmosphere of Titan, blowing up the base. While there, he brought along Professor Marius' dog K9 to fight the Swarm-infected humans. Unable to return to Earth with K9, Marius gave the Doctor K9 as a gift. (DW: The Invisible Enemy)

The Doctor later traced the source of a Time Hole to where a group of scientists had been experimenting on a skull called Eustace. Much to his horror, the Doctor found that "Eustace" was actually the skull of a Fendahl Golden Core, but managed to stop a cult from nearly causing the end of the world. He later tossed the skull into a star to be rid of it and its evil once and for all. (DW: Image of the Fendahl)

The Doctor later helped the people of a Pluto colony rebel against the Company, that was oppressing them with high taxes, even saving a person from committing suicide. (DW: The Sun Makers)

. (DW: I am the Doctor)

. (DW: I am the Valeyard)

The Doctor helped what remained of the original Minyans locate their race bank and home planet. He also defeated the Oracle, a machine that had been selfishly ruling the planet in place of its populace. (DW: Underworld)

Lord President of Gallifrey
Returning once more to Gallifrey and, posing as vainglorious and power-mad, the Doctor sought and attained the office of 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 K9 and Andred, a Gallifreyan in the Chancellory Guard she had fallen in love with. However, the Doctor left the Capitol with K9 Mark II, in a crate, planning to continue adventures with his beloved dog. (DW: The Invasion of Time)
 * The Doctor and K9 Mark II spent an indeterminate period of time together. However, in the next episode, DW: The Ribos Operation, he appeared to be activating K9 Mark II, giving the impression that no significant time had elapsed since leaving Gallifrey, though he could have possibly been repairing him.

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)

While the Doctor and Romana searched for the Key, they were twice interrupted by outside sources emitting chronometric radiation that disrupted the tracer's ability to work, in the form of a chronometric pulse caused by a breach in the higher dimensions (PDA: Tomb of Valdemar) and a network of spatial teleportation paths created by a malfunctioning time cabinet intersecting with Earth's ley lines. (MA: The Shadow of Weng-Chiang) After these two encounters, the Doctor and Romana took a long break from searching for the Key. (PDA: Heart of TARDIS)

During this break, the Doctor, Romana, and K9 encountered a frog-like being named Bolog, who had a fleet of ships at his command. The Doctor was able to stop him with a banana. (DWM: Death to the Doctor!)

Later, the Time Lords contacted him, telling him that they needed him to go on a mission. The Doctor, however, left them after relearning that the Brigadier was in danger, after he was captured by a terrorist group. The Doctor discovered an Avatar universe that had the Second Doctor, Jamie McCrimmon, and Victoria Waterfield trapped inside. Afterwards, they were forced to continue with the quest. (PDA: Heart of TARDIS)

The Doctor and Romana finally 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 with the help of the Key while it was assembled. (DW: The Armageddon Factor) Afterwards, Romana regenerated and the two, along with K9, continued to travel together. (DW: Destiny of the Daleks)

Romana II
Forgetting Romana was only to be with him for the quest for the Key, the Doctor decided to bypass the randomiser and take himself and Romana on a relaxing holiday to Paris in 1979. There, the Doctor discovered that a Jagaroth named Scaroth had been splintered into twelve selves throughout time after his spaceship exploded, which led to the creation of life on Earth through the radiation from the exploding ship that affected the primordial ooze. The Doctor, Romana and detective Duggan succeeded in stopping Scaroth from preventing his spaceship from exploding, which would have undone life on Earth. (DW: City of Death)

The Doctor later received a distress signal and arrived on Chloris, a lush and verdant world with only small quantities of metals, all of which were controlled by its ruler, Lady Adrasta. The Doctor was sent for execution, but managed to avoid it, deciding to investigate the creature he was supposed to be fed to. He found it to be an imprisoned Tythonian that had been sent by its people to set up a trade agreement with Chloris. Deciding to end Adastra's tyranny, the Doctor allowed the Tythonian to kill her and let a new reign of peace be set up between the two species of the planet. (DW: The Creature from the Pit)

The TARDIS then arrived on the space liner Empress, which had become locked together with a private ship, the Hecate, after colliding with it upon emerging from hyperspace. The Doctor and Romana met Tryst, who had a Continuous Event Transmuter machine. However, some Mandrels from Eden had somehow gotten onboard. The Doctor later discovered he had been lied to and the supposed addictive drug vraxoin was actually a valuable material that the Mandrels decomposed into. The Doctor thwarted the plan of Tryst and the pilot of the Hecate, separated the two ships, and returned the Mandrels to Eden. (DW: Nightmare of Eden)

Whilst in the middle of conducting TARDIS repair, the Doctor and Romana were caught in the middle of a sacrificial ceremony for a "god" called the Nimon. They discovered that this "god" was actually a parasite alien preparing Skonnos for the rest of its species. The Doctor succeeded in preventing the teleport from bringing more than two extra Nimon before the Nimon killed themselves as an accidental side-effect to their final gambit. With the help of the Anethans originally sent to be life-force sacrifices for the transporter, the Doctor destroyed the remaining Nimon before departing with Romana. (DW: The Horns of Nimon)

Tired of his constant unknown travels, the Doctor took a break in Brighton Beach, but landed in the wrong season to do so. At Romana's urging for a technologically advanced place of relaxation, the Doctor took them to the Leisure Hive, where the remaining Argolins ran it. However, during the adventure to repair a rejuvenation machine, the Doctor ended up ageing hundreds of years. A genetically created Argolin named Pangol decided to take over, but thanks to the Doctor's interference, his plan to create a clone army of himself backfired as the Doctor was in the machine beforehand, gaining his youth back. However, the Doctor had to remove the randomiser in order to repair the machine, deciding that he had enough of running. (DW: The Leisure Hive)

Arriving on Tigella after repairing K9 from their previous adventure/vacation, the Doctor and Romana found themselves trapped onboard the TARDIS in a time loop by the last of the Zolfa-Thurans, Meglos, who also took the Doctor's form after attaching itself to a humanoid body to help itself steal the power of Dodecahedron. However, the Doctor was successful in redirecting the death beam Meglos had pointed at Tigella back on him after escaping the time loop. (DW: Meglos)

Travels in E-Space
While trying to return to Gallifrey to take Romana back and reunite with Leela, the Doctor was taken by surprise when the TARDIS entered a pocket universe called E-Space. During this time, the Doctor picked up a new companion, Adric, who was nearly just as intelligent as he was. (DW: Full Circle)

The Doctor eventually found a way to leave E-Space through a new opening at zero coordinates, but to his displeasure, Romana chose to stay behind to help liberate enslaved Tharils with K9. (DW: Warriors' Gate)

Return to N-Space
Following his return from E-Space with Adric, the Doctor was in an increasingly morose and dark mood due to missing Romana. He was called by the Traken Union's Keeper to assist him in keeping evil away while his power waned from age and a replacement Keeper was found. The Doctor was successful in preventing the still decaying Master from obtaining ownership of the Source, but was unable to prevent him from stealing the body of Councillor Tremas. (DW: The Keeper of Traken)

Tired of the TARDIS' chameleon circuit being stuck as the police box, the Doctor decided to measure one and give the numbers to the people on Logopolis to fix it. However, he was impeded in his task by the newly reborn Master and was temporarily shrunk down along with the TARDIS due to a mathematical error. However, this error was quickly rectified and the TARDIS was reborn, minus the still malfuctioning chameleon circuit. During the fight, he picked up two additional companions, Tegan Jovanka and Nyssa. Much to the Doctor's horror, the Master had stopped all computations on Logopolis for too long; the universe had needed Logopolis to survive past its natural end and CVEs were the only thing allowing the universe to continue. The Doctor decided to form a shaky alliance with the Master to use the Pharos Project Radio to open a new CVE and save the universe. (DW: Logopolis)

Death
Despite having saved the universe, the Doctor knew the Master would try to make the situation work for him and was correct when he found the Master was going to blackmail the universe into servitude in exchange for its continued existence. Successful in making the CVE permanently open, the Doctor fell from the Pharos Project radio telescope to the ground, hundreds of feet below, after disconnecting a wire.


 * "It's the end. But the moment has been prepared for."

- Last Words of the Fourth Doctor

Though his companions were greatly worried about him, the Doctor told them the moment had been prepared for. The Watcher, which had been tracking him through time and space and was an apparition of his next incarnation, merged with him and the Doctor regenerated. (DW: Logopolis)

Undated events

 * Presumably by himself, the Fourth Doctor visited Leela's home planet, encountered the supercomputer Xoanon and inadvertently installed in him a copy of his own personality. (DW: The Face of Evil)
 * The Fourth Doctor attended the funeral of Alistair Gordon Lethbridge-Stewart. (ST: The Gift)
 * The Fourth Doctor and Azmael had an encounter in which Azmael drank so much that the Doctor had to throw him into a pool to sober him. (DW: The Twin Dilemma)
 * The Fourth Doctor met Winston Churchill in 1879, posing as a Punch and Judy man whilst hunting Cybermats. (REF: The Brilliant Book 2011)

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Personality
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Behind the scenes

 * Actors considered for the role of the fourth incarnation included Michael Bentine, Bernard Cribbins, Graham Crowden, Fulton Mackay and Jim Dale.
 * Tom Baker was cast based on his role as the villain Koura in The Golden Voyage of Sinbad.
 * According to the creators of the show and Baker, the character's look was originally based on paintings and posters by Henri de Toulouse-Lautrec of his friend, Aristide Bruant, a singer and nightclub owner whose trademark was a black cloak and long red scarf.
 * The fourth incarnation's distinctive appearance and mannerisms have made him a target for affectionate parody.