Throughout the 60-year history of Doctor Who, The Doctor has come up against some frightening enemies, some of which have remained constant threats. The Cybermen, The Master, and the iconic Daleks all reappear on a regular basis to up the stakes when The Doctor is in peril. Of all of these villains, the Daleks are the most famous. They are indiscriminate killing machines who can't be reasoned with, and whose sole purpose is to exterminate anything that isn't Dalek.