While Doctor Who’s depiction of a Dalek willing to betray its species in Jodie Whittaker’s final episode may seem like a direct refutation of the antagonists’ established characterization, the seeds for this story were planted 47 years earlier. Traditionally, the Daleks are Doctor Who’s most infamous alien baddies, constantly bothering the Doctor across time and space. Very occasionally, however, the Doctor and a Dalek have seen eye-to-eyestalk. Doctor Who’s traitorous Daleks include the hybrid Dalek Sec, and Rusty, introduced in 2014 during the Twelfth Doctor’s tenure.
The idea that the Doctor and his oldest enemies could get along was taken even further during Jodie Whittaker’s farewell episode,