Kralls

 Name: Kraals

 Format: Television Show and Audio

 Time of Origin: Attacked Earth in the 1970s.

 Appearances: "The Android Invasion", behind-the-scenes in "Trail of the White Worm" before appearing in full in "The Oseidon Adventure".

 Doctors: Fourth Doctor

 Companions: Sarah Jane Smith, Harry Sullivan, Platoon Under-Leader Benton and Leela

 History: A particularly subtle and manipulative race, the Kraals were notable in that they had a far more stealthy plan of attack than the usual alien strategy of a direct assault against key resources, implementing a long-term infiltration plan to eliminate those most likely to successfully oppose their conquest of Earth from the inside.

 Physically, the Kraals were humpbacked, gargoyle-like humanoids with lumpy, grey skin, unusual facial ridges and a rhinoceros-like horn, generally seen wearing striped tunics that were presumably their equivalent of a uniform (The Doctor noted that they have endured radiation exposure for approximately twelve centuries, making it unclear if this is their natural appearance or the result of prolonged mutation from exposure to the radiation).

Kralls

 The Kraals had a wide variety of technological devices, with the most popular of these being their androids. These androids were made in the form of a specific person, generally a human. They had most of the memories of the subject, but were bullet-proof and loyal to the Kraals. To create these androids the Kraals had to scan the subject's brain, or someone who had dealt with the subject. This scan was very painful and could cause brain damage if it went on for too long, but could provide sufficient detail for the Kraals to recreate an entire Earth village to the point that even The Doctor didn't notice anything wrong with the location at first.

 As well as androids, the Kraals also had advanced genetic modification techniques and replication techniques, allowing them to create a deadly virus and construct an artificial duplicate of areas of Earth to use as a testing ground for their androids.

 The Kraals lived on a doomed world, as their naturally-radioactive planet, Oseidon, was becoming more radioactive, with radiation reaching critical levels that would prohibit them from remaining on it, requiring them to find a new world that they could inhabit.

 They abducted a human astronaut, Guy Crayford, and won his allegiance by claiming that he had been abandoned by humanity after his ship suffered an accident, using information taken from his brain to create several human-like androids - focusing on creating duplicates of people who would be likely to oppose their invasion of Earth, including members of UNIT such as The Doctor's old companions Harry Sullivan and now-Platoon Under-Leader Benton - and an entire British village from his memory. After testing these androids, they planned to send them to Earth with a deadly virus to infect and kill all of the humans, the virus subsequently burning itself out within three weeks and allowing the Kraals to emerge and rule.

 Fortunately, the Fourth Doctor and Sarah Jane Smith discovered the Kraal plot when the TARDIS materialised in the artificial village the Kraal were using to prepare the androids, witnessing some of the Kraal androids in action as the Kraal prepared for their assault. Having made contact with Guy Crawford while trying to infiltrate the control area of the village in the nearby duplicate of a Space Defence Station, The Doctor and Sarah were forced to steal Crawford's old rocket when the TARDIS returned to Earth without them in order to warn their friends and avert the planned invasion. Despite the Brigadier's absence and the presence of android doubles of The Doctor and Sarah, The Doctor was able to stop the androids by using the Space Defence Station's radar dish to broadcast a signal that disrupted their ability to operate, further aided when Sarah convinced Crawford that the Kraals had been manipulating him after revealing that his supposedly missing left eye was completely intact under his eyepatch. With Crawford distracting the Kraal leader, Styggron, The Doctor attacked Styggron himself by reprogramming his own android duplicate to turn against the Kraal, stopping Styggron before he could release the virus while infecting Styggron with the virus himself, although both Crawford and the android Doctor were shot in the process.

Kralls

 During the Kraals' second invasion attempt, they allied themselves with The Doctor's old enemy the Master - his currently-crippled form ("Legacy of the Daleks") having been temporarily revitalised by energy absorbed from the Eye of Harmony ("The Deadly Assassin") -, the Master travelling to Earth to track down an ancient worm that had been hidden in Derbyshire centuries ago, seeking the creature's ability to generate wormholes ("Trail of the White Worm") so that he could create a wormhole to the Kraal homeworld ("The Oseidon Adventure"), most likely officially requesting their aid in repairing his body later. Although the Kraals immediately betrayed the Master after they reached Earth and imprisoned him with The Doctor's current companion Leela while interrogating The Doctor, the Master and Leela were able to escape through the wormhole to the Kraal bunker, where they learned that the Master with Leela was an android duplicate; the real Master was posing as Kraal Chief Scientist Tyngworg, currently interrogating The Doctor.

 With the distraction caused by the arrival of the android Master and Leela, The Doctor escaped his own captivity, reprogramming the androids to destroy the invasion force, but the Master realised when trying to deactivate the androids that he was another duplicate, created so that the real Master could carry out his true plan; by recovering a Z-battery that The Doctor had left on Earth during his exile, the Master intended to combine its Z-radiation with Osedion's O-radiation to create ZO-radiation and renew his damaged body. Using the reprogrammed android Master - and aided by Kraal Marshal Grimnal, the only survivor of the Kraal invasion force -, The Doctor was able to have the duplicate kidnap the original and take it away in the Master's TARDIS before he could complete his plan. Although Grimnal was shot by Colonel Spindleton, a former ally of the Master, after the Master's defeat, his actions still saved Oseidon, leaving the Kraals to work on healing their own planet rather than conquering others.

 To date, the Kraals and The Doctor have not confronted each other again, although a group of Slitheen ("Aliens of London/World War Three") that the Ninth Doctor was imprisoned with in the twenty-fifth century ("The Monsters Inside") noted that they have sometimes disguised themselves as Kraal, suggesting that the Kraals eventually found a way to survive their planet's damaged state.