20th century On Earth , the 20th century , recorded as 2 . 0K by the 43rd century dating system , ( AUDIO : " The Torchwood Archive " ) was one of the most turbulent , violent , yet progressive centuries in the planet ' s history . In addition to major conflicts including the First ( TV : " To the Last Man " ) and Second World War s , ( PROSE : " Players " ) humankind began to explore beyond their homeworld for the first time , and also began to make huge leaps in technological advancement . ( TV : " Day of the Moon " ) It was also during the 20th century that many world governments learned of the existence of extraterrestrial lifeforms . ( AUDIO : " Storm Warning " , TV : " Spearhead from Space " ) According to many accounts the general public also learned of alien life , ( COMIC : " Invaders from Gantac ! " , " The Mark of Mandragora " , PROSE : " The Dying Days " ) although other accounts indicate they remained in the dark about this until the beginning of the 21st century . ( TV : " Aliens of London " ) Numerous alien defence organisations came to power in this century , including the Torchwood Institute , ( TV : " Fragments " ) the Forge , ( AUDIO : " Project : Twilight " ) LONGBOW , ( PROSE : " Just War " ) Counter - Measures , ( TV : " Remebrance of the Daleks " ) C19 , ( PROSE : " Who Killed Kennedy " ) HAVOC , ( PROSE : " The Showstoppers " ) UNIT , ( TV : " The Web of Fear " , " The Invasion " ) MIAOW , ( PROSE : " The Dreadful Flap " ) P . R . O . B . E . , ( HOMEVID : " The Zero Imperative " ) and UNISYC . ( PROSE : " Interference " ) The Modular s believed that Earth in this era was a complete temporal mess due to the high amounts of aliens and time travellers . The planet was constantly being destroyed , replaced , removed from history , but the timelines somehow always stablisied . ( PROSE : " Elementary , My Dear Sheila " ) The Doctor had a great affinity for this century , though his first incarnation initially claimed to tolerate but not enjoy it . ( TV : " An Unearthly Child " ) However , his granddaughter Susan Foreman believed that he had a fondness for the 20th century as he often visited it on their travels together . ( AUDIO : " The Alchemists " ) He lived during this time period for several years as an exile from Gallifrey ( during his third incarnation ) , ( TV : " Spearhead from Space " " Doctor Who and the Silurians " , et al . ) and again for a number of months in 1913 and 1969 in his tenth incarnation ( to name just two examples ) . ( TV : " Human Nature " / " The Family of Blood " , " Blink " ) Many of the Doctor ' s Earth companion s came from this century , as he visited it often . ( TV : " An Unearthly Child " , " The Massacre of St Bartholomew ' s Eve " , " The War Machines " , " Spearhead from Space " , " Terror of the Autons " , " The Time Warrior " , et al . ) At some point in the 20th century , the Fisher King invaded the planet Tivoli and was there for ten years . The native Tivolian s were liberated by the Arcateenian s , but later enslaved by the very same race . ( TV : " Before the Flood " ) It was also among the centuries endured by Ashildr , a 9th century Viking girl who was rendered effectively immortal when she was brought back to life by the Twelfth Doctor through a self - repairing Mire repair kit . ( TV : " The Girl Who Died " ) By the year 3012 , the 20th century was considered ancient history . ( PROSE : " Festival of Death " )