Robot Yeti

Robot Yeti were servitors created by the Great Intelligence, originally as protectors before using them as an army. They may have been based on living Tibetan Yeti. However, because no living Yeti were ever definitively studied, it was also possible that the robotic Yeti was the source of the myth.

Appearance and Construction
The Yeti robots were large and hairy to disguise themselves in the Himalayas. Their claws, feet, and eyes were the only parts not covered in fur; their claws and feet were black and bumpy, their teeth yellow, and their eyes green. The "Mark I"s were bigger and more bear-like, whereas the "Mark II"s in London had better-defined hands capable of wielding web-guns. These Yeti had flaps at their chest which hid the control spheres that provided their motive power, serving as a brain. Yeti could also be directed somewhere through the use of a locus. Until activated, Yeti could stand immobile for long periods, completely shutdown and unaware of what went on around it. When instructions did arrive it would come to life and begin moving. (TV: The Abominable Snowmen, The Web of Fear)

The "Mark III" Yeti retained the same appearance but were the result of New World University's research into nanotechnology and atomic engineering. A control sphere could plunge itself into a human chest, nano-instructions inducing immediate atomic restructuring and multiplication until the person became a Yeti. Whether this meant they were organic or cyborgs is unclear, but these Yeti had yellow fangs and were more susceptable to projectile fire. They could also fire web from their claws. (PROSE: Downtime)

History
There were previous "Snowmen" controlled by the Yetis Future master in Victorian London. (TV: The Snowmen)

The Yeti were created to serve the Great Intelligence (TV: The Abominable Snowmen), also known as the Great Old One Yog-Sothoth. (PROSE: All-Consuming Fire) A non-corporeal entity, the Great Intelligence took over the body of Padmasambhava, the lama of Det-Sen Monastery, and built the Yeti over hundreds of years. The Yeti were initially a ruse to scare off curiosity seekers from the mountain cave where the Intelligence planned to manifest; later, they became more of an army serving the Great Intelligence. These robots were similar in appearance to what explorer Professor Edward Travers called "real" Yeti.

20th century
The Second Doctor, a friend of Padmasambhava's, arrived in the Himalayas 1935 with his companions Victoria and Jamie. Along with Professor Travers, they put an end to the Great Intelligence's plan when Jamie smashed the pyramid control in the cave. (TV: The Abominable Snowmen)

More than forty years later, a formerly non-functioning robot Yeti on display in London was reactivated by a control sphere, subsequently somehow transforming into the "Mark II". Setting up a Yeti production plant in Wimbledon, (PROSE: Millennial Rites) the robots then covered London in webbing, forcing the evacuation of the populace. Later, in the Underground, Alistair Gordon Lethbridge-Stewart and his troops attempted to stop them, the Intelligence using the Underground as a nervous system. (TV: The Web of Fear) This event gave impetus to the formation of UNIT. (TV: The Invasion)

Lethbridge-Stewart again encountered a Yeti on Gallifrey, left over from Rassilon's games. On this occasion, the Second Doctor maddened it with a firework, and the resulting rock fall prevented any further interaction with it. It is not clear whether this was a robot or a live Yeti. (TV: The Five Doctors)

Establishing New World University by 1995, the Intelligence-controlled Victoria Waterfield utilised control spheres to find the final locus, which bound the Intelligence to Earth. These spheres turned several New World students into Yeti, which proceeded to battle UNIT to defend the generators powering the Intelligence, but were subseqently defeated once more through the combined efforts of Victoria, Sarah Jane Smith, and Lethbridge-Stewart. (HOMEVID: Downtime)

21st century
A Yeti sidearm was removed from the Hub, the underground HQ of Torchwood 3, following the Hub's destruction. It was then delivered to the CIA Special Operations Division who went rogue and stole the shipment. (PROSE: The Men Who Sold the World)

A Yeti was kept in Underbase 1 in 2010. (COMIC: The Age of Ice)

Other encounters
A group of Yetis were put in the Doctor's TARDIS by to battle the Graak. (GAME: Destiny of the Doctors)

At some point, explorers searching for the Yeti were captured by the Intelligence. A lama Gampo called the real Yeti to battle against the robots, defeating them. (COMIC: Yonder... The Yeti)

Alternative timelines
In an alternate timeline created by the Black Guardian where the First Doctor never left Gallifrey, and became Lord President, the Yetis were one of many forces that invaded Earth, and fought over the planet with invaders of various alien races. This timeline was destroyed when the Seventh Doctor retrieved the Key to Time. (COMIC: Time & Time Again)

In the pocket universe of the Great Kingdom, a trapped Intelligence used sheer will to transform the material around it into eight-foot-tall Yeti with red-brown fur animated directly by the Intelligence. (PROSE: Millennial Rites)

Continuity

 * Because no clear pictures exist of the supposed "real" Yeti seen at the end of The Abominable Snowmen, direct comparison of the Mark I and "real" Yetis, as televised, is impossible. However the novelisation does afford such a comparison: "It was taller and less bulky. The fur was longer and silkier, and had a more reddish tint. Above all, the face was different, rather like that of a lemur, with dark, soft eyes." Nevertheless, it is extremely unlikely that the brief wide shot that was included in the episode as broadcast would have been able to convey this level of detail. Indeed, this is an instance where the novelisation may be said to actively contradict the televised episode. Since episode six is missing, it is impossible to judge the reliability of this description.''
 * The date of the second Yeti invasion is the point at which the UNIT dating controversy begins. The script of episode two of The Web of Fear says that the events of Snowmen took place "in 1935" which is in turn said to be "over forty years ago". This means that "Web" has to take place no earlier than late 1975. Since Lethbridge-Stewart is only a colonel in Web, it means his next appearance in The Invasion, and all the subsequent ones must take place even later than 1975, well after Tom Baker had begun to play the Fourth Doctor in real life. However, episodes made under John Nathan-Turner, and particularly Mawdryn Undead, indicate that the UNIT stories all took place in more or less the year they were broadcast. Also, the semi-official UNIT website gives the date of the incident as 1968, the same year The Web of Fear aired. Hence, the Tenth Doctor eventually refers to his time working for UNIT as vaguely happening in the 1970s or 1980s. (TV: The Sontaran Stratagem)

Appearances in unmade stories
The Yeti would have reappeared in The Laird of McCrimmon, a story abandoned because of the Yetis' creators dispute with the BBC. This story would have seen the writing out of the character of Jamie McCrimmon. The Yeti would also have also appeared briefly in the planned 30th anniversary special The Dark Dimension in a scene deliberately echoing The Web of Fear.