Zygon

The Zygons were a race of metamorphic humanoids

Physical characteristics
Zygons are solidly built humanoids with large, cone-shaped heads. Their heads, arms and torsos are covered in suckers and they have deeply inset faces. Zygons have dark red blood and speak in a gurgling whisper. Zygons are stronger then humans and can live for several centuries. (DW: Terror of the Zygons)


 * Apocryphal information: Zygons also have a very deeply ingrained fear of fire. (Doctor Who and the Loch Ness Monster)''

Technology
Zygon technology is partly biological and all their technology has a half-grown look. This is shown by the Skarasen, a large creature from Zygor which has been cybernetically enhanced.

One of the most important device of the Zygon is their shapshifting ability. The Zygons can capture a Human and put them in special receptacles. They can then take the form of the human, but they need periodic bio-scan checks in order to maintain the illusion. Because of this, the subjects are kept alive but unconscious during the whole process. This process copied both the appearance and the voice of the subject, though the Zygon's actions may give them away. (DW: Terror of the Zygons)

Culture
Little is known about the Zygon culture, since the only Zygon shown were soldiers.

''Apocryphal information: they may measure sound in Remars. (DW: Doctor Who and the Loch Ness Monster)

History
The Zygons were originally at war with the Xaranti. During this war, both the Zygon homeworld, Zygor and the Xaranti home planets were destroyed. (PDA: The Bodysnatchers). Refugees were able to create a refugee fleet. One of the war-ships was damaged and eventually made it to Earth, where the Zygons hid in the Devil's Punchbowl in Scotland since at least the 12th century. They subsisted on the milk of the Skarasen, which they had brought in embryo form from their home planet and converted into a cyborg, which the Zygons controlled.

Sightings of the Skarasen would inspire legends of the Loch Ness Monster. waiting for news from their home. When, in the late 20th century they learned that Zygor was destroyed, they decided to take over Earth and physically adapt it to an environment more to their liking. UNIT and the Doctor stepped in, though in the meantime the Skarasen swam south from Scotland to London via the Thames. The status of the Zygon invasion fleet still headed to Earth remained unresolved, though by implication, it would take some time to arrive. (DW: Terror of the Zygons)

=References=
 * The Time Lord population of the prison Shada may possibly have contained a Zygon. (DW: Shada)


 * When re-united with the Doctor, the Brigadier remembered the Zygons, among other adversaries he had fought as head of UNIT. (DW: Mawdryn Undead)


 * The Doctor used "the Zygon gambit and the Loch Ness Monster in the Thames" as an example to Ace of the alien invasions that Humans has managed to rationalize away or forget. (DW: Terror of the Zygons)


 * The Doctor said that when he felt depressed, he would make clay models of Zygons to cheer himself up. (NA: Human Nature)


 * Though she did not recall the Zygons directly, Sarah Jane Smith boased to Rose Tyler that she had met the Loch Ness Monster. (DW: School Reunion)