Zygon

The Zygons were a race of metamorphic humanoids.

Physical characteristics
Zygons were solidly built humanoids with large, cone-shaped heads. Their heads, arms and torsos were covered in suckers, and they had deeply inset faces. Zygons had dark red blood and spoke in a gurgling whisper. They were stronger than humans and could live for centuries. (DW: Terror of the Zygons) They also had an earthy, iron smell and the ability to sting people with venomous barbs on their palms. (NSA: Sting of the Zygons, DWN: Doctor Who and the Loch Ness Monster)

Young Zygons were called hatchlings and were slimy and pale with shorter limbs. Hatchlings were mute, but much faster than adults. (NSA: Sting of the Zygons)

Zygons had a deeply ingrained fear of fire. (DWN: Doctor Who and the Loch Ness Monster) They could be easily hypnotised by a clock's swinging pendulum. (VG: Doctor Who: Destiny of the Doctors)

Technology
Zygon technology was partly biological in basis, with an organic look. This was exemplified by the Skarasen, a large creature from Zygor which was cybernetically enhanced. (DW: Terror of the Zygons) Their use of organic ships was well known. (EDA: Alien Bodies)

One of the most important Zygon discoveries was their body-print technology. The Zygons would capture a specimen, such as a Human, and put them in a special receptacle. A Zygon could then take the form of this specimen, mimicking both voice and appearance. This body-print needed to be renewed every 2 hours, which meant the prisoners were kept alive but unconscious. (DW: Terror of the Zygons) Though they generally took the forms of humanoids, they could also mimic creatures of different sizes and shapes, such as dogs and cattle. (NSA: Sting of the Zygons) A Zygon who could no longer transform was known as a Zynog. (BFA: Death in Blackpool)

In order to control the Skarasen, the Zygons used Trilanic activators. Zygons frequently used molecular dispersal to get rid of corpses. Their ships tracked the life-signs of the Zygons and would bring the body back to the ship if a Zygon was killed. (DW: Terror of the Zygons, NSA: Sting of the Zygons) They also made use of a type of nerve gas in order to render Humans unconscious. (DW: Terror of the Zygons) Another Zygon discovery was called the "amber sleep", which was a type of suspended animation. (NSA: Sting of the Zygons)

Culture
Zygons were divided into clans, which varied in habits. (BFA: The Zygon Who Fell to Earth) Zygon warlords were known to fight in elaborate shape-shifting duels using the bodies of other creatures held captive. (DWY: Rest and Re-Creation)

Zygons measured distance in remars. (DW: Terror of the Zygons, NSA: Sting of the Zygons)

History
In 102, the Zygons were among the races who joined the Alliance at Stonehenge. They came to Stonehenge and helped imprison the Doctor in the Pandorica in order to save the Universe. (DW: The Pandorica Opens)

At some point before the 12th century, a Zygon ship was damaged and was forced to land on Earth near Devil's Punchbowl in Scotland. They had a Skarasen with them, which, though still an infant at that point, provided them with the lactic fluid they needed to survive. (DW: Terror of the Zygons)

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, and the ship on Earth was contacted. (DW: Terror of the Zygons)


 * When this destruction of Zygor occurred is unknown.

Another ship from Zygor arrived on Earth in 1909. Though they had brought 2 Skarasen, their minds were damaged by the solar radiation brought on during the destruction of Zygor. One was killed during the attempt to repair the damage. Though the Zygons attempted to conquer Earth anyway, due to starvation -- and the actions of the Tenth Doctor -- they were forced to abandon their plans. (NSA: Sting of the Zygons)

In the late 20th century, the Zygons of Devil's Punchbowl decided to take over Earth and physically adapt it to an environment more attuned to their species. UNIT and the Fourth Doctor stepped in and were able to stop them, letting the Skarasen free at the same time. (DW: Terror of the Zygons)


 * The status of the Zygon invasion fleet still headed to Earth remained unresolved, though by implication, it would take some time to arrive.

In December 1985, a Zygon landed in Antarctica, near UNIT Arctic base Skywatch-7. Several people stationed there were killed, but the survivors were able to drive it into the water. (DWM: Skywatch-7)

The Graske also kidnapped a Zygon, implying there were Zygon Changelings. (DW: Attack of the Graske)

Undated events

 * The Master using the power of the planet Siralos was able to transport some Zygons as well other adversaries to The Doctor's TARDIS in an effort to stop Graak from saving the imprisoned seven incarnations of the Doctor. (VG: Doctor Who: Destiny of the Doctors)
 * The Divine Empress had Zygons under her command. (EDA: Genocide)