Doctor Who: The Underwater Menace

"The Underwater Menace" is the title to a four-part serial from the 1960s British science fiction television series Doctor Who. It is the twenty-ninth serial in the series and features William Hartnell as the First Doctor in his 129th-132nd appearances on the series. The storyline is notable as being the last major work for William Hartnell on the series, though he will return for the four-part serial, "The Three Doctors" in 1972-1973. It is also notable for the introduction of the Cybermen, who will go on to become major recurring antagonists throughout the show.