History of the Daleks

The Daleks (/ˈdɑːlɛks/ DAH-leks) are a fictional extraterrestrial race of mutants from the British science fiction television series Doctor Who. The mutated remains of the Kaled people of the planet Skaro, they travel around in tank-like mechanical casings, and are a race bent on universal conquest and destruction. They are also, collectively, the greatest alien adversaries of the Time Lord known as the Doctor, having evolved over the course of the series from a weak race to monsters capable of destroying even the Time Lords and achieving control of the universe.

The First Doctor first encounters the Daleks in the second serial of the show, The Daleks (1963−64). In this version of Dalek history, the Dalek home-world Skaro is described by the Daleks in the second episode as having once been home to two humanoid races: the Daleks and the Thals. Following a short but terrible nuclear war between the races "over five hundred years ago", the Thals were horribly mutated and the "Dalek forefathers" retired into the city. According to the Thals in the third episode, the Daleks were originally teachers and philosophers, while the Doctor states in the fourth episode that the Daleks were called Dals back then, and speculates that the Daleks had just as badly been mutated at the time. They are more or less confined to their city; their motive power being electricity conducted via metal walkways. After discovering the anti-radiation drugs of the Thals kill them, the now-xenophobic Daleks decide to release radiation from their nuclear reactors into Skaro's atmosphere, leaving only the Daleks. However, the TARDIS crew convince the Thals to fight the Daleks to stop this. At the end of this serial, the Daleks are seemingly wiped out when their power source is destroyed. However, the popularity of the Daleks ensured their return.

...
Wikipedia