The Zygons are a fictional extraterrestrial race in the long-running British science fiction television series Doctor Who. They first appeared in the Fourth Doctor serial Terror of the Zygons.
The Zygons have shape-shifting abilities, allowing them to replicate the appearance of another being, but they must keep the subject alive in order to use its body print. This skill was vital in their concealment and in their scheme to seize power despite their small numbers.
The Zygons were also accompanied by an armoured cyborg creature called the Skarasen, the lactic fluid of which was necessary for them to feed. Broton planned to unleash the Skarasen (or Loch Ness Monster as it was known) on an energy conference in London as part of a bid to conquer the Earth.
The plan was foiled and both he and his crew were killed due to the intervention of Doctor Who and the UNIT, which caused the Skarasen to return to Loch Ness. Zygon technology is biological in nature: in essence their ships and equipment are actually alive.
The Zygons returned in the The Day of the Doctor 50th Anniversary Special on November 23, 2013, alongside the Daleks.
Meanwhile, tenth Doctor actor David Tennant has stated that they are his favourite monsters from Doctor Who.