The evil genius who created the Daleks is one of the Doctor's most formidable foes. A scientist from the planet Skaro, he created the Daleks in order to ensure the survival of his race and, ultimately, to help him become master of the Universe. In these episodes, the Fourth Doctor, Tom Baker, travels back in time in an attempt to prevent the Daleks from ever being created. But Davros returns to threaten the Earth once more in two episodes featuring David Tennant as the Tenth Doctor.