Daleks are a Alein race from the planet skaro known as the kaleds, they were origionaly were humanoid but a long lasting nuclear,chemical and biological war with the other sentient race on the planet( the thals) lead to the degeneration and eventual mutation of the kaled race, but kaled scientists prediced this and built armed and armoured "travel machines" for their future mutated descendants. but the evil and crippled scientist Davros started a production line creating artifical mutants to pilot his travel machines.
the other kaled scientists disaproved of this greatly, but davros was set in his ways of making a cyborg super race, so he sent a comunicae to the thals telling them he wanted an end to the mellenia spanning war along with information on how to destroy the protective dome over the last kaled city. the thals launched the most powerful nuclear weapon ever used against the kaled dome and destroyed the entire city and all of the remaining kaleds instantly.....except for davros who was hiding underground in his secret laboratory. he proceded to send a army of daleks to exterminate the thals which they did with conviction. after a conflict of intrest with the first dalek davros ended up being exterminated and the daleks became their own race.

eventualy the daleks left their scared homeworld with a vast army and conquered and enslaved everything they found.