It might surprise modern Doctor Who fans to know how much of the show's foundational lore didn't exist when it first began. Perhaps the greatest example of this is the very idea of the Time Lords and Gallifrey. While they were introduced quickly in the revival as facts of the universe, the Time Lords were first mentioned in 1969 and Gallifrey was not explicitly named for the first ten years of the Classic Era.
The history of Doctor Who's core cast of villains is similarly complex. While the Daleks appeared in the show's second serial, the Cybermen were not introduced until 1966, the Sontarans in 1973, and the Zygons in 1975. But one of the most interesting villains to appear later in the show's history is the Master.
The Master did not exist in the show until 1971, at which point he quickly became a central part of the Doctor's life and the audience's understanding of the Doctor's people. In total, the Master has appeared in 39 stories, made up of 100 distinct appearances. Over the next 7 slides, we discuss each actor who has held the role and which episodes they appear in.