An amphibious humanoid race, the Zygons are notable for their ability to metamorphose into other living forms, as well as their use of organic technology. Centuries ago, a spaceship full of Zygons crash-landed in Scotland. Unable to return to their native planet, which had been destroyed in a solar explosion, they planned to make Earth their new home. Using their shape-shifting powers and a sea monster called the Skarasen, their plans were foiled when their leader Broton was shot by UNIT. The Skarasen returned to live peacefully in Loch Ness.
As an anniversary present, the Eleventh Doctor took Amy and Rory to the Savoy Hotel on 26 June 1890. Unfortunately, half the staff turned out to be Zygons in disguise.
Their obsession with Earth continued when they managed to infiltrate UNIT causing a stand-off between humanity and the alien race. But this peace accord did not last long, and Zygon factions split off causing a possible war. Thankfully, the Twelfth Doctor managed to talk down Bonnie (a Zygon who had taken the form of Clara) and UNIT's Kate Stewart.