Davros & The Daleks in Doctor Who.
In the original series in 1963 (infact the 2nd ever Doctor Who story) the Daleks are clearly introduced as being the survivors of a great war, so mutated by radiation they can only exist inside a special casing (The Dalek machine), confined and never ever being able to leave their city.
Jump forward 14 years to Tom Baker and the Genesis of the Daleks, the Timelord's take the Doctor back in time to the creation of the Daleks, so he may prevent their construction. Where we meet Davros, who is purposefully mutating the Kaled people to place inside the Dalek machines to create his dream master race. A cool episode, but totally at odds with the early canon. In particular the orginal Daleks can only travel inside their city using static electricity as an energy source, but in Genesis, they are clearly shown moving around outside in the wastelands exterminating people.