Kraal ( species ) The Kraals were a race of technologically advanced humanoid s native to Oseidon . The ever higher levels of radiation on their homeworld forced them to look for new planet s to inhabit . Technology . Styggron developed Kraal android s . They were created through the use of a pattern analyser , which implanted the memories and intelligence of a subject into an android , which then took on the form of its subject . They were nearly indestructible , but Styggron produced weaponry capable of destroying them . The analyser could also extract information to the Kraal data bank s . The Kraals also produced a virus that was both highly contagious and very deadly ; so much so that contact with it could prove fatal to a Kraal in seconds . ( TV : " The Android Invasion " ) History . The Kraals lived on a doomed world , evolving due to exposure to radiation over a dozen generations . ( AUDIO : " The Oseidon Adventure " ) Oseidon was becoming more radioactive , reaching critical levels which the Kraals could not withstand . They abducted a human astronaut , Guy Crayford , and scanned his brain . Styggron tailored his androids to look like the inhabitants of Devesham , an English village , which was also produced , along with the adjoining Space Defence Station , as a training ground on Oseidon . After testing these androids , they planned to send them to Earth with a deadly virus to infect and kill all of the humans . The Fourth Doctor used the radar dish es at the real Space Defence Station to disable the androids there and then boarded the rocket Styggron had used . Crayford confronted the Kraal about his lies , having promised that no humans would be harmed . Styggron killed him but was thrown by an android of the Fourth Doctor onto the steriliser containing the virus . He was infected but managed to fire his gun , destroying the android , before he died . ( TV : " The Android Invasion " ) With the help of , the Second Kraal Army attempted to invade the Earth again , by using a wormhole that the Master generated in Derbyshire . Upon arrival on Earth , the Kraals , led by Marshal Grinmal , double - crossed the Master and imprisoned him with Leela , while they sent the Doctor to Oseidon to be interrogated by Chief Scientist Tyngworg . Grinmal allied himself with the Master ' s former ally , Colonel Spindleton , as they drew out their battle plans . Grinmal allowed Spindleton to take possession of Great Britain after the invasion , in exchange for knowledge to conquer the world . However , while this was going on , the Master and Leela escaped through the wormhole , and infiltrated the Kraal bunker . However , while he was in the bunker , the Master discovered he was an android duplicate , ever since he arrived in Derbyshire , and the Master had been on Oseidon all along , impersonating Tyngworg . During this , the Doctor escaped and reprogrammed the androids to destroy the invasion force . But , as the Master tried to deactivate all the androids , he discovered he was susceptible to the signal , and therefore , he had also been an android all along as well . After the destruction of the Second Kraal Army and the androids , Grinmal was the only surviving Kraal . He allied himself with Leela and the Doctor , so he could stop the Master ' s real plan , which involved destroying Oseidon . While trying to stop the plan , Grinmal was shot by Spindleton , but the Master ' s plan was foiled . ( AUDIO : " The Oseidon Adventure " ) The Slitheen family sometimes disguised themselves as Kraals in their attempts to make money . ( PROSE : " The Monsters Inside " ) Behind the scenes . According to " The Brilliant Book 2012 " , a , in 1881 they attempted to replace Prince Bertie with an android duplicate , but the Doctor and Jenny stopped them .