Fourth Doctor

"Would you like a jelly baby?"

-The Fourth Doctor, Filled with wanderlust and a renewed curiosity towards exploring time and space, the Fourth Doctor left all ties of his previous incarnation's exile behind on Earth, setting off to travel the universe, taking advantage of his freedom once more.

This incarnation of the Doctor initially travelled with Sarah Jane Smith and Harry Sullivan, but Harry chose to remain on Earth when the opportunity arose. The Doctor and Sarah 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 the time.

After tangling with the Master on Gallifrey when he tried to heal himself and renew his regeneration cycle, 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 of Vardans, 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 Lady Romana and K9 Mark II. Once that search was concluded, the Doctor and Romana went on the run from the Black Guardian. Not long after, Romana regenerated into a new body and continued to travel with the Doctor and K9. When they attempted to answer a Gallifreyan summons, the trio accidentally passed into the smaller universe of E-Space.

During his travels in E-Space, the Doctor gained a new companion in the teenaged mathematical genius Adric. Romana and K9 stayed behind in E-Space as the Doctor and Adric departed for N-Space. There, they encountered a Trakenite named Nyssa and a human named Tegan. The foursome successfully prevented the destruction of the universe by the Master, but only at the cost of this incarnation's life.

The Doctor prepared for the worst when the Watcher, an entity born of his own immediate future, appeared to warn him of his demise. Due to the Master messing with the rotation controls for the Pharos radio telescope, the Doctor fell a great height. Suffering terrible injuries, he was assisted by the Watcher in his last moment, who joined with him and helped him regenerate into his next incarnation.

Post Regeneration
The Third Doctor's death took place ten years after the radiation from the Great One's lair caused severe damage to his body. He returned to Earth to end his time in the company of Sarah Jane and the Brigadier. K'anpo Rimpoche soon arrived and kick started the regeneration. Once he had regenerated, the Doctor suffered delirium, mumbling random things from his past adventures, and was physically exhausted. He was put in sickbay, where medical officer Harry Sullivan kept watch on him. However, the Doctor managed to outwit him and get to his TARDIS to leave. Slipping away from UNIT HQ, the Doctor visited a planet colonised by the Mordee expedition, and encountered the colony ship's powerful computer, Xoanon, which he repaired from damage Xoanon sustained, accidentally imprinted his own mind on the computer, leaving him with multiple personalities. He also visited Pesca, and encountered the Pescaton leader, Zor. Returning to UNIT HQ, though still with situational awareness issues, the Doctor was asked by the Brigadier to help deal with the 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 returned to travelling in his TARDIS, taking Sarah Jane and Harry with him, abandoning a UNIT dinner party at Buckingham Palace and leaving without telling the Brigadier.

Travels with Harry and Sarah
Due to Harry's inadvertent interference with the helmic regulator, the TARDIS landed on Space Station Nerva, where humanity had been cryogenically suspended to await Earth's recovery from solar flares. There, the Wirrn wished to use the humans as food and incubators for their kind after the human race had destroyed their breeding colonies throughout the Andromeda galaxy in a thousand-year battle with them, sending them into space. Unable to reproduce without terrestrial colonies, they sent their queen to the Nerva Beacon, who birthed several larvae before she died from the Nerva Beacon auto-guard. The larvae began to feast on humans, absorbing their knowledge and their bodies. Luckily, Noah, a human was converted into a Wirrn, retained his strong will and tricked the Wirrn into a suicide. Afterwards, on behalf of the space station, the Doctor went down to Earth with Harry and Sarah Jane to fix the transmat relay, leaving the TARDIS on the station, while Vira, the station's first medtech, tended to waking the rest of her crew from their long sleep

Once on Earth, they found the Sontaran Styre conducting experiments on humans as a prelude to an invasion. Caught in the wrong place at the wrong time, the Doctor was accused of murdering a GalSec officer among a crew who had been lured to the Earth and slowly picked off by Styre. After escaping them, he rescued Sarah from an experiment where her inner fears were used against her. Styre appeared to fatally shoot the Doctor as he fled, but the Doctor had nicked a piece of the Nerva's synestic locking system, which guarded him from injury. Knowing a Sontaran would not refuse an opportunity to engage in mortal combat, the Doctor returned and challenged Styre to a duel. This wore him out and bought Harry enough time to remove a terullian diode bypass transformer from the ship that nurtured Styre with energy, making the energy feed on Styre instead. The Doctor went on to address the Marshal who had sent Styre to Earth. The Doctor defeated his plans by bluffing the Marshal to call off his attack, allowing the resettlement of Earth to proceed, and transmatted with his companions back to the space station to retrieve the TARDIS.

Intercepting their transmat beam, a Time Lord messenger appeared to the Doctor and forced him to undertake a mission on the Time Lords' behalf: prevent the creation of the Daleks or induce them to develop into less aggressive creatures. The messenger also gave the Doctor a Time Ring, which he could use to get back to his TARDIS. Upon their arrival on Skaro, the Doctor, Sarah Jane and Harry was caught up in a war between the Kaleds and Thals, with the Doctor being taken prisoner by the Kaleds with Harry after being separated from Sarah Jane. While being questioned, the Doctor met the creator of the Daleks, a scientist named Davros, attempting to genetically engineer the Kaleds as the effects of their weapons caused them to mutate, seeking to evolve their mutations into a perfect form. Despite respecting each other as scientists, the Doctor was unable to convince Davros to change the Daleks into better creatures.

When he revealed he knew of several defeats of the Daleks in the future due to faults in their design, the Doctor was forced to tell Davros of each failure the Daleks suffered, so that he could prevent them. Attempting to gauge the extent of his insanity, the Doctor posed a question to Davros, asking him what he would do if he possessed the power to end all other life. Davros's willingness to utilise such power horrified the Doctor, tempting him to cut off his life supports as a last resort of stopping his plans, but he was prevented from doing so by Nyder, and he was imprisoned. Escaping, the Doctor destroyed Davros' recording of the foreknowledge, thus keeping the future from changing for the worse. The Doctor found little other option left than to ensure the Daleks would never exist, and had the opportunity to blow up the stock of embryonic Daleks that Davros had produced. However, he questioned if he had the right to destroy the Daleks, knowing that wiping out an entire species would make him just like them, and the fear of the Dalek had caused many worlds to ally with each other. With this in mind, the Doctor allowed the Dalek species to persist, and chose to stall their rise to power instead. Failing to listen to the Doctor's warnings, Davros found his own creations usurping him.

Because they were programmed to acknowledge any creature as inferior to the Dalek, they deemed him unworthy to rule them. Fleeing after the Daleks killed Davros, the Doctor buried them and their factory underground, delaying their progression by a thousand years. After departing from Skaro, the Doctor, Sarah Jane and Harry became scattered across the Adelphine Cluster due to a temporal disruption interfering with the time ring. However, they were eventually united by the interventions of the Time Lords, who also provided them with a replacement time ring. Using the time ring, the Doctor, Sarah and Harry set off for Space Station Nerva. But instead, they arrived on the Desolii, a famous ghost ship, where they encountered friendly robots, microscopic psychiatrists and ghost. Due to the interference of the CIA, the Doctor, Harry, and Sarah Jane returned to the Space Station Nerva earlier in its time line, when it orbited Jupiter, which had a fifty-year assignment to guide space freighters. The TARDIS was travelling back through time to them, leaving them stranded until it arrived. While waiting for it to arrive, the Doctor became involved with stopping a Cyberman attack on Voga, the planet of gold, to keep the resource of their major weakness to a minimum in the Cyber-Wars. The Doctor ultimately stopped them from blowing up the planet, defeating them once more. Finally reunited with the TARDIS, the Doctor received a call for help from the Brigadier via a space-time telegraph. The Doctor, Sarah and Harry met up with the Brigadier, and discovered that an alien race known as the Zygons were planning to use a Skarasen to attack London and abducting people to power body-prints that let them shape-shift into the forms of humans as disguises, the disappearance of the Duke of Forgill being among them. The Doctor and company had several close calls with the Zygons and eventually discovered the location of their spaceship, rescuing everyone, during which, the Doctor instigated the ship to self-destruct.

Discovering the plan was to have the Skarasen besiege Stanbridge House in a display of power, the group made haste to London. As the Brigadier and UNIT took care of the surviving Zygon commander, Broton, the Doctor found the trilanic activator used to control the Skarasen's movement and gave it to the Skarasen, who ate it and returned to Loch Ness. The Doctor prevented the destruction of the city, though the monster was still seen by the populace, and the Brigadier would have to quietly cover up the incident. After returning to Scotland to retrieve the TARDIS and bring the Duke back home, Harry chose to leave the TARDIS and find a more conventional means of transportation, while the Doctor managed to persuade Sarah to stay.

Adventures with Sarah
The Doctor and Sarah Jane next landed on Zeta Minor, thirty-thousand years in the future. Accused of killing the crew attempting to mine the planet for alternative sources to replace their dying sun, the Doctor instead found that the planet was the boundary between the normal universe and the anti-matter universe; taking any mineral from the planet would trap a ship there. The crew's leader, Professor Sorenson, had been infected with anti-matter and was fighting off its influence as he kept changing back and forth into a monster that mummified living beings. The Doctor tricked Sorenson into the TARDIS and kicked him into the pool of anti-matter, releasing the expedition ship and restoring the professor to normal. The Doctor and Sarah Jane posed as Earth delegates on the planet Farrash, a dying planet that official Earth delegates took no interest in. During a public demonstration, the Doctor was separated from Sarah Jane and became caught up in a protest against "baby killing". The Doctor learned the Leader was sanctioning the abortion of foetuses in order to supply his scientists with the neurochemicals their experiments to save Farrash required. One scientist created a mechanical body that swiftly became a rogue robot and went on a killing spree. The robot fell through the ground and became trapped underneath civilisation. With the Leader killed, the Doctor encouraged the population to work together to find a way of saving Farrash, and left with Sarah Jane. The Doctor and Sarah next visited London in 1666, with Sarah Jane falling victim to the Black Death. Before he could save her, the Doctor was held responsible for the Great Fire of London by Sergeant George Mullens, despite helping locals to put it out. However, he escaped a lynch mob and cured Sarah back at the TARDIS. Attempting to return to UNIT, the Doctor instead arrived at a priory in 1911, on the future site of UNIT headquarters. There, he had to prevent the last of the Osirans, Sutekh, from escaping his prison in Egypt and destroying the universe. Though unsuccessful in stopping Sutekh's servant, Marcus Scarman, from releasing him, the Doctor was able to delay Sutekh's trip through a time corridor to the priory by moving the corridor's threshold to the far future, thus effectively ageing him to death. Not realising his actions would cause the thermal balance to equalise, the Doctor accidentally set the priory on fire. After landing near a manor house in 1764, the Doctor nearly drowned in a frozen lake while following giant cat footprints. He was rescued by Rector Adams, and decided to remain when he and Sarah saw a 20th-century double decker bus in the woods. Adams invited them to accompany him to Lady Huntingdon's ball, where the Doctor was reunited with Iris Wildthyme and learnt the bus was actually her TARDIS.

He discovered Iris intended to marry off her companion, Edwin Turner, to Lady Huntingdon's granddaughter, Bella, so that she would inherit the estate. When the Rector was killed by a giant animal, the Doctor discovered Huntingdon and Bella were actually shape shifting cat aliens who wanted to steal Iris' TARDIS. Bella turned against Huntingdon, and before Huntingdon could hijack Iris' TARDIS, the Doctor trapped her in a pocket dimension with the use of a Time Lord dimensional message capsule. Afterwards, the Doctor and Iris went their separate ways again. Holidaying at the ruins of Phaester Osiris with Sarah, the Doctor was kidnapped by archaeologist Edwin Carver, and stopped him and the cult of the Black Pyramid from awakening Horus. He destroyed the Black Pyramid afterwards to prevent Horus from ever returning. Afterwards, the Doctor seemingly found himself in a town Sarah Jane had previously visited for a newspaper article. They ultimately found that it was a facsimile of the town, not even actually on Earth, 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. Discovering Sarah had been replaced by an android, the Doctor found and rescued her. With the help of Harry Sullivan and UNIT, the Doctor was able to stop the aliens and rescue the townsfolk the Kraals replaced. After he and Sarah Jane returned to UNIT HQ, the Doctor based himself on Earth, staying at his old cottage and resuming use of Bessie, while Sarah Jane continued working as an investigative reporter. However, the two frequently took trips in the TARDIS, and were often accompanied by Harry. While working with UNIT, the Doctor started to write a series of educational books called Doctor Who Discovers. The intended title for the series was The Doctor, Who Discovers..., but the publishing company misprinted the title, resulting in the author being mistakenly credited as "Doctor Who". The Doctor completed five books in the series. He began researching the Princes in the Tower for the sixth book, Doctor Who Discovers Historical Mysteries, but left it unfinished. Whilst the Doctor was conducting an experiment at his cottage, the TARDIS began to dematerialise. Realising it was being taken away by a time warp, the Doctor managed to devise a way to jam it enabling him and Sarah to board it. As the TARDIS was diverted to a space station in the Milky Way, the Doctor sabotaged the time circuits and fell into a deep coma. To force him to awake to repair his ship, Shazar, the rogue Time Lord who had masterminded the event, threatened Sarah. The Doctor awoke to save Sarah Jane and Shazar revealed his alliance with the Daleks, ordering the Doctor to repair the TARDIS so the Daleks could use it to complete the time circuits of their own fleet of TARDISes. The Doctor tricked Shazar into leaving the station to collect cirenium, as the Doctor anticipated he was quickly tracked down by the Time Lords. The Doctor and Sarah evaded the Daleks until Shazar returned with cirenium, believing he’d convinced the Time Lords that the Doctor was the one allied with the Daleks, which cuadwdcaused the Dalek TARDISes’ Destruction upon being installed. The Time Lords rescued them from the Dalek space station, revealing they’d realised the Doctor’s plan for the cirenium all along. The Doctor accidentally landed the TARDIS in a swamp on Diamedes, where he meet the gentle, dim-witted Slodes and saved them from swamp creatures. Attending another UNIT Christmas party, the Doctor was unable to prevent a Voddod ship from crashing to Earth. Aided by Sarah Jane and Harry, the Doctor raced to find Brac, the crashed alien warrior, before UNIT troops found and killed him. On another mission for the Time Lords, the Doctor was sent to destroy a space station that held the Bendriggans' virus. However, he and Sarah were accused of murdering a messenger and sentenced to death by Admiral Cosmicon, the Bendriggan commander. The Doctor proved his innocence by sending a message in Time Lord logic to a Bendriggan code expert. But winning their trust was short-lived when many Bendriggans became infected. After watching the Admiral die, the Doctor set the Bendriggan flagship on collision course with the space station, destroying them both and saving the remainder of the Bendriggan race. Diverted by the Time Lords again, the TARDIS arrived in Italy in 1944 where the Doctor and Sarah were initially suspected of being German spies. When a German convoy arrived, Father Antonio hid them in his church and revealed it held a number of treasures including a genuine painting by Raphael. Convincing Antonio that he was time traveller by showing him the TARDIS, aided by the Time Lords shifting the TARDIS forward to 1976, the Doctor and Sarah helped Antonio by hiding the church’s treasures onboard when the German soldiers came for them. They took the TARDIS forward it in time to 1948, returning the treasures to Antonio. The Doctor and Sarah Jane relaxed back on Earth for a few days afterwards, until the Doctor read about Sir Julian Hubert’s excavation of Hubert’s Folly. Enlisting the aid of the Home Secretary, he rushed to stop the excavation but was too late. He revealed to Julian that he’d helped his great-great-uncle seal up an explosive engine that he’d created, which was now firing energy. Together he and Julian attempted to defuse it but were unsuccessful. Instead they arranged for the military to seal it again with quick-drying cement. The Doctor found his TARDIS forced to land on Karn by the Time Lords, as the Sisterhood of Karn had been crashing ships that passed Karn to protect what was left of their Elixir of Life. The Doctor used a firecracker to unplug the crevice the elixir came from, being promptly booted out. He then discovered the evil Time Lord Morbius was being resurrected in a patchwork body. Defeating him in battle of mindbending, the Doctor managed to reduce Morbius to a mindless beast that tumbled off a cliff to his death. However, the Doctor was left severely drained, but the Sisterhood allowed him to drink some their elixir, which restored the Doctor's health. Being summoned by UNIT on behalf of the World Ecology Bureau, the Doctor saw pictures of a pod discovered in Antarctica. The Doctor and Sarah were flown to Antarctica, and found that the pod was Krynoid and had infected Charles Winlett. Outside, they also found another pod, and put it in the freezer. Before they could do anything for Winlett, he mutated further and became aggressive, going on a rampage. While trying to stop the new Krynoid, the Doctor failed to stop Scorby and Keeler, who worked for Harrison Chase, from finding the other pod, and escaping with it.

After the Krynoid was destroyed by Scorby's bomb, the Doctor and Sarah were rescued, and brought back to England. Investigating Chase Manor, the Doctor and Sarah encountered the Krynoid, who had infected Keeler, and had taken control of the body of Harrison Chase, planning to spread its seeds to take over Earth. While fighting Chase, the Krynoid and the plants animated by the creature, the Doctor called in UNIT, who worked with the RAF to destroy the Krynoid and the manor along with it. The Doctor and Sarah visited London to find that the Pescatons were invading Earth. The Doctor discovered their weakness to high-pitched noise and set a trap for their leader, Zor, killing him. When he died, all the other Pescatons died as well. After they failed to aid the survivors of a devastated Earth, the Doctor honoured Sarah's request to go somewhere they could "make a difference" and took her help him to kill a baby destined to grow up into a dictator. However, after the Sixth Doctor failed to kill the baby, the Fourth Doctor realised a different solution, and alerted the baby's mother to the Eighth Doctor's attempt on her child's life. While the Fourth Doctor helped his eighth incarnation escape, the baby's mother realised her love for her child, and decided to raise them better. During a trip in space, the Doctor accidentally brought the Helix Intelligence to San Martino, Italy, in the 15th century, where it planned to dominate the human race by using the Brotherhood of Demnos as its agents. Because the agents had been converted into pure energy beings by the Helix, the Doctor tricked the Brotherhood's leader, Hieronymous, into using all his energy until he vanished. Using his mask and cloak, the Doctor posed as him and used a device to drain the energy out of the rest of the Brotherhood, killing them and saving the Earth. Whilst Christmas shopping in 1980s New Zealand, Sarah and many other shoppers were kidnapped, along with a large percentage of turkeys. Investigating, the Doctor discovered the Hazoodians were using turkeys to make alcohol. Realising the humans were being kidnapped by accident, the Doctor returned them to Earth. The Doctor made another visit to Vortis, where he found the crystalline Clynex was draining the energy from its surroundings and attracting the Menoptera to their deaths. The Doctor saved them from Clynex by shattering it with his sonic screwdriver. The TARDIS' steering went out, causing the ship to go back in time forty-five-hundred-million years. The Doctor and Sarah observed Earth, at the time a mass of molten rock, develop into a world with an atmosphere and life. They also encountered Megron, a Lord of Chaos claiming to be ruler of Earth until the Doctor banished him. The TARDIS landed in an English quarry, where it was buried by an explosion. The Doctor emerged unscathed, but Sarah was taken ill and so he accompanied her to hospital. There, he discovered she had come into contact with a stone hand and, when Sarah stole the hand and fled, followed her to Nunton Experimental Complex. Her wearing of a ring brought her under the control of Eldrad, a Kastrian scientist. The Doctor used a cooling duct to reach Sarah and brought her to her senses.

Eldrad restored herself using the reactor core. The Doctor agreed to take her back to Kastria, her homeworld, but only in the present, not her home time, as this broke the Laws of Time. On Kastria, Eldrad was injured by an acid-laden booby trap, so the Doctor and Sarah had to conduct her to a regenerator chamber. There she was restored to her male form. Eldrad discovered his people to be dead and asked the Doctor to return him to Earth so he could rule over humanity. Fleeing from him, the Doctor made use of his scarf, with Sarah holding the other end, to trip Eldrad, who fell into an abyss. Back in his TARDIS, the Doctor received a telepathic summons from Gallifrey and was forced to leave Sarah behind, just as she herself had decided to return home. They both agreed they wouldn't forget one another as Sarah left, but the Doctor had accidentally left her in Aberdeen, Scotland instead of South Croydon.

Returning to his home
Discovering that the signal hadn't come from someone he knew, the Doctor returned to Gallifrey, just as it was the time of the election for Lord President, and theorised that the departing President was in danger. Stealing a robe to blend in, the Doctor attempted to prevent an assassination, but ended up framed for murdering the Lord President. To keep himself from being executed, the Doctor declared his own candidacy for Lord President. Believing the Matrix would give him clues as to who was behind this, the Doctor ended up in a mental duel with the culprit. After finding the assassin, the Doctor learned that it was Goth, another Lord President candidate, who was being manipulated by the Master; since their last meeting, the Master, with no regenerations left, had degenerated into a rotting corpse. The Master was plotting to use the Eye of Harmony in an attempt to restart his cycle of regenerations by using the Sash of Rassilon to protect himself from the effects of the Black hole that would destroy Gallifrey as a side-effect.

After failing to convince the Master that, since the sash was damaged in the death of the old president, it would put the Master at risk, the Doctor fought him off. Though the Master managed to escape capture, the Doctor left his former teacher, Borusa, to lead Gallifrey as Cardinal, though, as the only candidate left, he was still eligible to gain the title of Lord President, even after leaving.