- You may be looking for the Rutan spy Karne.
Though once a "flourishing" empire, Karn was reduced to a wasteland of ruins by the civil war and following extinction of the Masters of Karn (AUDIO: Seven Keys to Doomsday) in a galactic war. (PROSE: Save Yourself) It was partially rebuilt by the Time Lords' colonisation, but, following the defeat of Morbius, Karn had once again become a burned-out and exhausted planet, a barren and rocky wasteland with many ruins and abandoned industrial plantations. It was littered with the wreckage of crashed spaceships from many worlds, brought down by the Sisterhood's telekinetic powers out of fear of theft of the Elixir of Life. (TV: The Brain of Morbius)
Karn was the first place to pop into the Eleventh Doctor's head when he tried to think of the rainiest, wettest, stormiest place he had ever been so he could compare it to the storms created by the Cybermen in Klimtenburg, but then he decided Margate made for a better comparison than Karn. (PROSE: Plague of the Cybermen)
According to certain accounts, Karn was originally a colony of the old Gallifreyan Empire in the days before Rassilon. These accounts suggest that the Sisterhood of Karn existed on Karn even then, a remnant of the Pythias who once ruled Gallifrey before being expelled by the triumvirate of Rassilon, Omega, and the Other. (PROSE: Cat's Cradle: Time's Crucible)
Under the Masters of Karn
In the distant past, Karn was the home of a species known as the Masters of Karn, whose civilisation was described by the Doctor as "the mightiest empire the galaxy had ever known". The Masters became interstellar conquerors, ruling hundreds of planets with the Citadel of Karn as their capital, until a civil war broke out among themselves at the peak of their power, culminating in an atomic catastrophe that collapsed their civilisation, leaving only primitive bands of brigands and farmers roaming what remained of the planet. At some point before their fall, the Masters created the Crystal of All Power, an extremely powerful device; fearing its power for destruction, they split it into seven parts, scattered across the planet. (AUDIO: Seven Keys to Doomsday)
A planet in ruins
Following the catastrophe, Karn was left a "shattered ruin", populated with mutated lifeforms of "nasty" disposition, such as the Clawrantulars, monstrous, sentient humanoid crabs who hunted by scent and could learn to use firearms. The Citadel was abandoned, with the central Computer not seeing a living being enter the innermost Citadel for a thousand years. Most of the land was unspoiled, however, allowing the survivors of the catastrophe to live on as peaceful farmers who had forsaken technology. (AUDIO: Seven Keys to Doomsday)
The Daleks' Doomsday Plan
Nearly a thousand years after the Computer had last seen a living being enter the Citadel, an army of Daleks led by the Emperor Dalek descended upon Karn, seeking to rebuild the Crystal of All Power and use it to power the Ultimate Weapon and thus rule the universe. They looted ruined cities, enslaving the natives to do so, and managed to locate two of the seven shards of the Crystal. However, the Karn inhabitants organised a resistance, which stole the two crystals and obtained a few more of its own.
An undated incarnation of the Doctor visited Karn in this time period, and stumbled upon a crystal. He took it onboard his TARDIS, unaware of its true nature, and was killed for his trouble, regenerating into an all-new form. Thereby learning of the Daleks' threat, the Time Lords assumed remote control of the Doctor's TARDIS, sending him back to Karn so that he may foil the Daleks' plans. The Doctor, alongside first-time companions Jimmy Forbes and Jenny Wilson, joined forces with a portion of the resistance. The Daleks eventually wrenched all seven crystals from them, but not before the Doctor had made some "alterations" to the molecular structure of the seventh crystal. As a result, the Ultimate Weapon went into overload and exploded after the Daleks charged it, taking all the Daleks on Karn (and what remained of the Citadel) with it while the Doctor and his companions escaped in the nick of time. (AUDIO: Seven Keys to Doomsday)
The Sisterhood and Morbius
By the time of the Rassilon Era, Karn had frequent relations with neighbouring planet Gallifrey, and the Sisterhood of Karn guarded the Sacred Flame. The Sacred Flame was used to distill the Elixir of Life, which could aid a Time Lord who experienced difficulty with regeneration. Morbius, a renegade Time Lord, in his bid for galactic conquest, came to Karn with a mercenary army. The Time Lords cornered him there, defeated, tried and supposedly executed him. However, Mehendri Solon, a human surgeon belonging to the Cult of Morbius, managed to secretly remove Morbius' brain. He preserved it and vowed to resurrect him. Solon settled on Karn in a disused hydrogen plant and sought a way to make Morbius live again. He used the body parts from dead crew members of different species' crashed ships to create a crude, grotesque new body for him. The Fourth Doctor and his companion Sarah Jane Smith stumbled across this plot after the Time Lords redirected the Doctor's TARDIS to the planet. The Doctor defeated Morbius, killing Solon in the process. (TV: The Brain of Morbius) Under Ohica's command, the Sisterhood of Karn attempted to give the wounded Morbius immortality, but they were defeated by Iris Wildthyme. (PROSE: Verdigris)
During the Last Great Time War
The Sisterhood remained on Karn. Their leader, Ohila, anticipated the Doctor's return in hopes he could stop the war then raging across creation. The Eighth Doctor, responding to an emergency distress signal from a gunship that had been damaged in orbit, attempted to rescue the sole remaining crewmember, a woman named Cass, but was ultimately killed when the ship crash-landed. The Sisterhood restored him to life for only a few minutes, allowing him to regenerate into his next incarnation. (TV: The Night of the Doctor)
The Doctor remained on Karn for sometime to recover, during which a war front began to approach the planet. Ohila allowed two Time Lords, Cardinal Rasmus and Commander Sanmar to come to Karn to repair the Doctor's TARDIS, unaware Sanmar was under orders to transport the heart of Karn to the Capitol. The Doctor, Rasmus and Ohila discovered her plan and stopped her. The Doctor threatened to use her equipment to destroy the planet, forcing Sanmar's superior, the Sixth Tamasan, to agree to protect the planet from the war front with a time lock. Before the time lock was put in place, the Sisterhood made Karn disappear with their own powers, which the Doctor and Rasmus believed they could have done all along but wanted to ensure the Doctor became who wanted first. (AUDIO: Light the Flame)
After the Last Great Time War
Karn and the Sisterhood survived the Last Great Time War. (WC: Prologue) Colony Sarff visited Karn in their search for the Twelfth Doctor on behalf of Davros. Ohila ordered Sarff to deliver his message to her and leave. Unbeknownst to Sarff, the Doctor had already arrived on Karn and was listening in. (TV: The Magician's Apprentice) Afterwards, the Doctor and Ohila discussed Davros's invitation, and he left his confession dial with her. (WC: Prologue)
In a negated timeline, Cristophe Zarodnix purchased Karn from the Sisterhood. From there he used a fragment of Morbius' brain and the genes of Straxus to recreate Morbius, who from there ruled an empire. When the Eighth Doctor turned off Morbius' Stellar Manipulator, the Time Lords prevented this Empire from forming, however, Morbius fell with the Doctor into a chasm, which still happened despite the timeline being prevented. (AUDIO: Sisters of the Flame/The Vengeance of Morbius) However, the Doctor was saved by the Sisterhood and transported to Orbis. (AUDIO: Orbis)
During the Cybermen’s conquest of time, the Twelfth Doctor crash landed on Karn and asked Ohila to take him to the Sisterhood's back door to Gallifrey. Ohila was reluctant at first, but after the Cybermen began to attack the Sisterhood, she showed him to the door. After the Doctor went through it, Ohila sealed the door behind him, trying to protect Gallifrey from a Cyberman invasion, unaware they had already taken control of the planet and Rassilon. The Cybermen’s conquest of time was later undone by the Doctor and Rassilon. (COMIC: Supremacy of the Cybermen)
Behind the scenes
Karn originated in a theatrical play, Doctor Who and the Daleks in Seven Keys to Doomsday, written by Terrance Dicks. Dicks re-used the name in the script for The Brain of Morbius. The play featured an alternative Fourth Doctor.