Zygon

The Zygons are an extraterrestrial race in the long-running British science fiction television programme Doctor Who. The Zygons have shape-shifting abilities, allowing them to replicate the appearance of another being. They first appear in 1975's Terror of the Zygons, where they attempt to invade the planet alongside their Skarasen creature, which they need to survive and has, in the serial's setting, been mistaken for the Loch Ness Monster. They subsequently return in the 2013 episode "The Day of the Doctor", where, following an invasion attempt, Zygons are able to negotiate with humans to be able to live on the planet. The Zygons are subsequently integrated into society in human disguise in the 2015 two-part story "The Zygon Invasion" and "The Zygon Inversion". While many Zygons are content to live as humans, many younger Zygons radicalise into a splinter group known as Truth or Consequences and seek to unmask all Zygons across the globe, though a truce is eventually able to be negotiated.

The Zygons were conceived by writer Robert Banks Stewart and designed by James Acheson. Initially, their debut story was largely focused on the idea of the Loch Ness monster being an alien, with the Zygons being shifted to the main focus during development. Steven Moffat, the then-showrunner of Doctor Who's 2005 revival, was impressed by their initial story and sought to bring them back, developing a storyline regarding the Zygons on Earth that would touch on contemporary issues.