Which 1966 Doctor Who serial is titled The Ark?

The Ark is the title of a 1966 Doctor Who serial.

The Ark is a four-episode story from Doctor Who’s third season, starring William Hartnell as the First Doctor. The Doctor, Steven Taylor, and Dodo Chaplet arrive on an enormous spacecraft carrying the last humans and animals from a dying Earth. The ship is traveling toward a new home, making it a literal ark for humanity.

The story includes the Monoids, an alien species involved in the ark’s society and political tensions. It also uses a time-travel structure: the travelers first see the mission in one period and later return to find events changed.

The title is sometimes associated with Pandora because the serial’s story includes a mysterious container-like object and themes of preserved life, but it is not a direct adaptation of the Greek myth. Its source is the BBC science-fiction series Doctor Who.